diff --git a/experiments/COUPLED_CONVERGENCE_STUDY_2026-09-19.md b/experiments/COUPLED_CONVERGENCE_STUDY_2026-09-19.md
index 9308e47..c42ba2b 100644
--- a/experiments/COUPLED_CONVERGENCE_STUDY_2026-09-19.md
+++ b/experiments/COUPLED_CONVERGENCE_STUDY_2026-09-19.md
@@ -207,6 +207,19 @@ formula, but the sparse grid is not a replay of its adaptive line search.
 Remainder scalars are direct FEM observations; saved Jp, RHS and correction
 allow independent verification of the linear defect and merit slope.
 
+## Additional n=3 linear control, specified before execution
+
+The frozen n=3 combined gravity/surface-scalar candidate passes eta=.003
+in 41 iterations versus 99 for baseline, with 37.609 versus 51.077 Krylov
+seconds. Its construction raises total setup/solve/check cost to 65.629
+versus 53.169 seconds. This favorable iteration count cannot yet be assigned
+to the surface correction: the same-state n=3 gravity-only ablation is
+missing. Before recommending coarse-setup optimization, add exactly that
+control with the same snapshot, RHS, target and 300-iteration cap, and a
+fresh baseline. No additional raw trial grid is needed for this attribution.
+The isolated branch is `research/n3-linear-ablation-20260919`, with case
+manifest `convergence_linear_followup_cases_2026-09-19.json`.
+
 ## Completed matched gravity-path test
 
 The retained-artifact audit passes both six-update restarts. Both begin at
diff --git a/experiments/convergence_linear_followup_cases_2026-09-19.json b/experiments/convergence_linear_followup_cases_2026-09-19.json
new file mode 100644
index 0000000..745a37c
--- /dev/null
+++ b/experiments/convergence_linear_followup_cases_2026-09-19.json
@@ -0,0 +1,33 @@
+[
+  {
+    "id": "n3_late_gravity",
+    "arguments": [
+      "--index",
+      "3",
+      "--angular-momentum",
+      "0",
+      "--surface-prescription",
+      "harmonics",
+      "--surface-degree",
+      "4",
+      "--restart",
+      "160",
+      "--max-linear",
+      "300",
+      "--rtol",
+      "0",
+      "--atol",
+      "1e-12",
+      "--max-newton",
+      "0",
+      "--linear-tol",
+      ".003",
+      "--preconditioner-probe",
+      "--preconditioner-variant",
+      "gravity-schur",
+      "--restart-snapshot",
+      "../../diagnostics/coupled_convergence_2026-09-19/screen_v1/n3_J0_control/capture_7/physical_base.txt",
+      "--allow-unconverged-restart"
+    ]
+  }
+]