diff --git a/internals/checks/testing-conventions.toml b/internals/checks/testing-conventions.toml
index 4375f031c..2439649e9 100644
--- a/internals/checks/testing-conventions.toml
+++ b/internals/checks/testing-conventions.toml
@@ -15,7 +15,7 @@
 # its own config drops that phantom root; a change to decide.py's path list still
 # demands a receipt through the normal --scope internals/checks/src walk.
 [python]
-one_function_per_file = { max_lines = 15 }
+one_function_per_file = { max_lines = 12 }
 
 [python.coverage]
 fail_under = 100
diff --git a/packages/python/testing-conventions.toml b/packages/python/testing-conventions.toml
index ccb2e635a..c9a1b5fd9 100644
--- a/packages/python/testing-conventions.toml
+++ b/packages/python/testing-conventions.toml
@@ -10,7 +10,7 @@
 extra_scope = ["packages/rust/src", "packages/python/src"]
 
 [python]
-one_function_per_file = { max_lines = 15 }
+one_function_per_file = { max_lines = 12 }
 
 # Same floor as the root file, which this lane no longer reads.
 [python.coverage]
diff --git a/packages/ts/testing-conventions.toml b/packages/ts/testing-conventions.toml
index 9f07b4ede..68263d63d 100644
--- a/packages/ts/testing-conventions.toml
+++ b/packages/ts/testing-conventions.toml
@@ -11,7 +11,7 @@
 extra_scope = ["packages/rust/src", "packages/ts/napi"]
 
 [typescript]
-one_function_per_file = { max_lines = 15 }
+one_function_per_file = { max_lines = 12 }
 
 # Same floors as the root file, which this lane no longer reads.
 [typescript.coverage]
diff --git a/testing-conventions.toml b/testing-conventions.toml
index 973b003c5..5862a31b0 100644
--- a/testing-conventions.toml
+++ b/testing-conventions.toml
@@ -80,7 +80,7 @@ extra_scope = ["packages/rust/src"]
 # --- Python (scanned: packages/python/dirsql) ------------------------------
 
 [python]
-one_function_per_file = { max_lines = 15 }
+one_function_per_file = { max_lines = 12 }
 
 # Unit-only coverage floor (branch coverage on, matching the prior --cov-branch).
 # The default for a config-less python caller (internals/distcheck); the
@@ -99,7 +99,7 @@ branch = true
 # build_command field), with `rust_toolchain: true` on the caller supplying cargo.
 
 [typescript]
-one_function_per_file = { max_lines = 15 }
+one_function_per_file = { max_lines = 12 }
 
 # Unit-only coverage floor, per vitest metric.
 [typescript.coverage]