diff --git a/php-transformer/composer.json b/php-transformer/composer.json
index 6295acf0e..2268825f1 100644
--- a/php-transformer/composer.json
+++ b/php-transformer/composer.json
@@ -161,6 +161,7 @@
       "php tests/unit/conditional-native-button.php",
       "php tests/unit/form-physical-box-ownership.php",
       "php tests/unit/form-offscreen-submit-presenter.php",
+      "php tests/unit/form-submit-caption-box.php",
       "php tests/unit/runtime-declarations-streaming-hash.php",
       "php tests/unit/external-metric-declarations.php",
       "php tests/unit/runtime-script-evidence-analyzer.php",
diff --git a/php-transformer/src/HtmlToBlocks/Style/FormPresentationGraphBuilder.php b/php-transformer/src/HtmlToBlocks/Style/FormPresentationGraphBuilder.php
index 83e07aa18..1bfcc6bf1 100644
--- a/php-transformer/src/HtmlToBlocks/Style/FormPresentationGraphBuilder.php
+++ b/php-transformer/src/HtmlToBlocks/Style/FormPresentationGraphBuilder.php
@@ -36,6 +36,15 @@ final class FormPresentationGraphBuilder
     private const TYPOGRAPHY_PROPERTIES = array(
         'color', 'font', 'font-family', 'font-size', 'font-weight', 'letter-spacing', 'line-height',
     );
+    /** A button caption carrier also sets the caption's case. */
+    private const CAPTION_PROPERTIES = array(
+        'color', 'font', 'font-family', 'font-size', 'font-weight', 'letter-spacing', 'line-height', 'text-transform',
+    );
+    /** A block-level caption carrier fills its button, so its padding sizes the button box. */
+    private const CAPTION_BOX_PROPERTIES = array(
+        'padding', 'padding-top', 'padding-right', 'padding-bottom', 'padding-left',
+        'padding-block', 'padding-inline', 'padding-block-start', 'padding-block-end', 'padding-inline-start', 'padding-inline-end',
+    );
     /** How far a text-carrier search may walk before the search, not the cascade, gives up. */
     private const MAX_CARRIER_CANDIDATES = 256;
     private const CONTROL_CONTAINER_PROPERTIES = array(
@@ -497,7 +506,7 @@ function (array $selector) use ($controlsForCustomProperties): bool {
                     // or `<span>` inside it). Typography that carrier declares wins
                     // over the label's own for that text, property by property, so a
                     // provider label that renders the text directly keeps it.
-                    $carried = $this->carrierTypography($buttonCaption ? array() : $roles, $element, $analysis['rules'], $customPropertyAnalysis['rules'], $conditional);
+                    $carried = $this->carrierTypography($buttonCaption ? array() : $roles, $element, $analysis['rules'], $customPropertyAnalysis['rules'], $conditional, $buttonCaption && ! $this->hasPadding($styles));
                     if ( array() !== $carried ) {
                         $overridden = array_map(static fn (string $key): string => str_replace('_', '-', $key), array_keys(array_intersect_key($styles, $carried['styles'])));
                         foreach ( $provenance as $factIndex => $fact ) {
@@ -698,8 +707,9 @@ private static function assertRole(mixed $role, ?array $condition, bool $allowEm
      * @param list<array<string, mixed>> $customPropertyRules
      * @return array<string, mixed>
      */
-    private function carrierTypography(array $roles, DOMElement $label, array $rules, array $customPropertyRules, array $labelConditional = array()): array
+    private function carrierTypography(array $roles, DOMElement $label, array $rules, array $customPropertyRules, array $labelConditional = array(), bool $captionBox = false): array
     {
+        $properties = array_flip(array() === $roles ? self::CAPTION_PROPERTIES : self::TYPOGRAPHY_PROPERTIES);
         $excluded = array_values(array_filter(
             array( $roles['control'] ?? null, $roles['required_marker'] ?? null ),
             static fn (mixed $element): bool => $element instanceof DOMElement
@@ -709,13 +719,19 @@ private function carrierTypography(array $roles, DOMElement $label, array $rules
         $conditions = array_fill_keys(array_keys($labelConditional), true);
         for ( $element = $carrier; $element instanceof DOMElement && ! $element->isSameNode($label); $element = $element->parentNode instanceof DOMElement ? $element->parentNode : null ) {
             $matched = $this->matched($element, $rules);
-            $base = array_intersect_key($matched['base'], array_flip(self::TYPOGRAPHY_PROPERTIES));
+            $carried = $properties;
+            // The caption carrier's own padding sizes an unpadded button only
+            // when the carrier is block-level; inline padding leaves the line box.
+            if ( $captionBox && $element->isSameNode($carrier) && self::isBlockLevelDisplay((string) ($matched['base']['display']['value'] ?? '')) ) {
+                $carried += array_flip(self::CAPTION_BOX_PROPERTIES);
+            }
+            $base = array_intersect_key($matched['base'], $carried);
             $conditional = $this->effectiveConditional($matched['conditional'], $matched['base']);
             foreach ($base as $property => $fact) {
                 foreach (FormCustomPropertyResolver::conditionsChanging($fact['value'], $element, $customPropertyRules, true) as $condition) $conditional[json_encode($condition)][$property] ??= $fact;
             }
             foreach ( $conditional as $encoded => &$facts ) {
-                $facts = array_intersect_key($facts, array_flip(self::TYPOGRAPHY_PROPERTIES));
+                $facts = array_intersect_key($facts, $carried);
                 if ( array() !== $facts ) $conditions[$encoded] = true;
             }
             unset($facts);
@@ -759,6 +775,20 @@ private function carrierTypography(array $roles, DOMElement $label, array $rules
      * @param list<array<string, mixed>> $rules
      * @param list<array<string, mixed>> $customPropertyRules
      */
+    private static function isBlockLevelDisplay(string $display): bool
+    {
+        return in_array(CssValueInspector::comparable($display), array( 'block', 'inline-block', 'flex', 'inline-flex', 'grid', 'inline-grid', 'flow-root' ), true);
+    }
+
+    /** @param array<string, string> $styles */
+    private function hasPadding(array $styles): bool
+    {
+        foreach ( $styles as $key => $value ) {
+            if ( str_starts_with($key, 'padding') && 1 !== preg_match('/^(?:0(?:\.0+)?(?:px|em|rem|%)?\s*)+$/', trim($value)) ) return true;
+        }
+        return false;
+    }
+
     private function carryFieldGroupGapOntoLabel(array &$row, DOMElement $control, array $ancestors, array $rules, array $customPropertyRules): void
     {
         if ( isset($row['label']['styles']['margin_block_end']) || isset($row['label']['styles']['margin_bottom']) ) {
diff --git a/php-transformer/tests/unit/form-submit-caption-box.php b/php-transformer/tests/unit/form-submit-caption-box.php
new file mode 100644
index 000000000..53bf76cf0
--- /dev/null
+++ b/php-transformer/tests/unit/form-submit-caption-box.php
@@ -0,0 +1,53 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * A submit whose caption is painted by a block-level inner carrier takes its
+ * box from that carrier: an unpadded `<button>` around a padded block
+ * `<span>` is as tall as the span. The presentation graph carries the
+ * carrier's padding and text case onto the button so a provider button,
+ * which renders the caption directly, keeps the source box and case.
+ */
+
+require dirname(__DIR__, 2) . '/vendor/autoload.php';
+
+use Automattic\BlocksEngine\PhpTransformer\HtmlToBlocks\Style\FormPresentationGraphBuilder;
+
+$failures = 0;
+$passes = 0;
+$assert = static function (bool $ok, string $message, string $detail = '') use (&$failures, &$passes): void {
+    if ( $ok ) {
+        ++$passes;
+        return;
+    }
+    ++$failures;
+    fwrite(STDERR, 'FAIL: ' . $message . ( '' !== $detail ? ' - ' . $detail : '' ) . PHP_EOL);
+};
+
+$submit = static function (string $css): array {
+    $document = new DOMDocument();
+    $document->loadHTML('<?xml encoding="utf-8" ?><body><form class="f" method="post"><input type="text" name="name"><button type="submit" class="btn"><span class="inner">Send</span></button></form></body>', LIBXML_NOERROR | LIBXML_NOWARNING);
+    $graph = (new FormPresentationGraphBuilder())->build($document->getElementsByTagName('form')->item(0), array(), $css);
+    return array( 'styles' => array_column($graph['controls'], null, 'index')[1]['control']['styles'] ?? array(), 'variants' => $graph['variants'] ?? array() );
+};
+
+$block = $submit('.btn { padding: 0; background-color: #f5a623; } .btn .inner { display: block; padding: .625em 1.9375em; text-transform: uppercase; font-weight: 700; }');
+$assert('.625em 1.9375em' === ($block['styles']['padding'] ?? null), 'a block carrier pads the unpadded button', json_encode($block['styles']));
+$assert('uppercase' === ($block['styles']['text_transform'] ?? null) && '700' === ($block['styles']['font_weight'] ?? null), 'the carrier sets the caption case and weight', json_encode($block['styles']));
+
+$inline = $submit('.btn { padding: 0; } .btn .inner { padding: 4px 8px; text-transform: uppercase; }');
+$assert('0' === ($inline['styles']['padding'] ?? null), 'an inline carrier leaves the button box alone', json_encode($inline['styles']));
+$assert('uppercase' === ($inline['styles']['text_transform'] ?? null), 'an inline carrier still sets the caption case', json_encode($inline['styles']));
+
+$padded = $submit('.btn { padding: 10px 20px; } .btn .inner { display: block; padding: 4px; }');
+$assert('10px 20px' === ($padded['styles']['padding'] ?? null), 'a padded button keeps its own box', json_encode($padded['styles']));
+
+$responsive = $submit('.btn { padding: 0; } .btn .inner { display: block; padding: 4px; } @media (min-width: 600px) { .btn .inner { padding: 12px; } }');
+$patches = array_map(static fn (array $variant): array => $variant['style_patch'] ?? array(), array_filter($responsive['variants'], static fn (array $variant): bool => 1 === ($variant['index'] ?? null) && 'control' === ($variant['role'] ?? null)));
+$assert('4px' === ($responsive['styles']['padding'] ?? null) && in_array('12px', array_column($patches, 'padding'), true), 'a conditional carrier padding becomes a variant', json_encode(array( $responsive['styles'], $patches )));
+
+if ( 0 < $failures ) {
+    fwrite(STDERR, "form submit caption box FAILED: {$passes} passed, {$failures} failed\n");
+    exit(1);
+}
+echo "form submit caption box passed: {$passes} assertions\n";