diff --git a/src/CelerisLab/lbm/kernels/operators/block_collision.cuh b/src/CelerisLab/lbm/kernels/operators/block_collision.cuh
index 9c436a9..a0e6234 100644
--- a/src/CelerisLab/lbm/kernels/operators/block_collision.cuh
+++ b/src/CelerisLab/lbm/kernels/operators/block_collision.cuh
@@ -1,10 +1,12 @@
+// CelerisLab – operators/block_collision.cuh
 // The one collision extension point of the blocked steps (BlockStep, BlockChannelStep).
-// Compile-time selection: MRT shares one path; SRT keeps two explicit arithmetic
-// variants, unchanged from their original kernels:
-//   level  (BLOCK_ROOT_BC 0/1): unclamped omega, no forcing term; shifted storage
-//          builds feq from the retained drho and direct momentum (numerical variant);
-//   channel (BLOCK_ROOT_BC 2): matches uniform OneStep SRT arithmetic (omega clamp,
-//          zero Guo forcing term, compute_feq).
+// Unforced by construction: FixedPatchStepper supplies no forcing, so no runtime
+// d_params.fx/fy branch is read. Two compile-time arithmetic families:
+//   uniform-equivalent (MRT on every level; SRT on the channel root, BLOCK_ROOT_BC 2):
+//          collide_dispatch arithmetic with zero force and no LES: clamped omega;
+//          SRT keeps the zero Guo forcing term of collide_srt;
+//   level SRT (BLOCK_ROOT_BC 0/1): unclamped omega, no forcing term; shifted storage
+//          builds feq from the retained drho and direct momentum (numerical variant).
 #ifndef CELERIS_OPERATORS_BLOCK_COLLISION_CUH
 #define CELERIS_OPERATORS_BLOCK_COLLISION_CUH
 
@@ -16,17 +18,19 @@
 #endif
 
 __device__ __forceinline__ void block_collide(float* f) {
-#if COLLISION_MODEL == 2
-    collide_mrt_unforced(f);
-#elif BLOCK_ROOT_BC == 2
-    float rho, ux, uy, feq[NQ], forcing[NQ] = {};
+    float rho, ux, uy;
     compute_rho_u(f, rho, ux, uy);
-    compute_feq(rho, ux, uy, feq);
+#if COLLISION_MODEL == 2 || BLOCK_ROOT_BC == 2
     const float omega = fminf(OMEGA_COLLISION_MAX, fmaxf(OMEGA_COLLISION_MIN, d_params.omega));
+  #if COLLISION_MODEL == 2
+    collide_mrt_no_force(f, rho, ux, uy, omega);
+  #else
+    float feq[NQ], forcing[NQ] = {};
+    compute_feq(rho, ux, uy, feq);
     collide_srt(f, feq, forcing, omega);
+  #endif
 #else
-    float rho, ux, uy, feq[NQ];
-    compute_rho_u(f, rho, ux, uy);
+    float feq[NQ];
 #if USE_DDF_SHIFTING
     // Preserve the density perturbation before adding the unit reference.
     const float drho = f[0]+f[1]+f[2]+f[3]+f[4]+f[5]+f[6]+f[7]+f[8];
diff --git a/src/CelerisLab/lbm/kernels/operators/collision_mrt.cuh b/src/CelerisLab/lbm/kernels/operators/collision_mrt.cuh
index 80d4637..efc59c1 100644
--- a/src/CelerisLab/lbm/kernels/operators/collision_mrt.cuh
+++ b/src/CelerisLab/lbm/kernels/operators/collision_mrt.cuh
@@ -114,16 +114,6 @@ __device__ __forceinline__ void collide_mrt_no_force(float* __restrict__ g,
     collide_mrt(g, rho, ux, uy, Fin, omega);
 }
 
-// Unforced MRT with the clamped device omega, as in collide_dispatch with zero
-// forcing. Shared by the blocked, channel-root and dense-patch collisions.
-__device__ __forceinline__ void collide_mrt_unforced(float* __restrict__ g)
-{
-    float rho, ux, uy;
-    compute_rho_u(g, rho, ux, uy);
-    collide_mrt_no_force(g, rho, ux, uy,
-        fminf(OMEGA_COLLISION_MAX, fmaxf(OMEGA_COLLISION_MIN, d_params.omega)));
-}
-
 #elif LATTICE_MODEL == LATTICE_D3Q19
 
 __device__ __forceinline__ void collide_mrt(float* __restrict__ g,
diff --git a/tests/unit/test_refinement_mrt.py b/tests/unit/test_refinement_mrt.py
index 02e2614..5a61a0d 100644
--- a/tests/unit/test_refinement_mrt.py
+++ b/tests/unit/test_refinement_mrt.py
@@ -32,22 +32,22 @@ class RefinementMRTHost(unittest.TestCase):
                      "collide_srt_no_force(f, feq, d_params.omega);"):
             self.assertIn(text, block_collision)
         self.assertIn("collide_srt(f, feq, forcing, omega);", block_collision)
-        self.assertIn("#elif BLOCK_ROOT_BC == 2", block_collision)
+        self.assertIn("#if COLLISION_MODEL == 2 || BLOCK_ROOT_BC == 2", block_collision)
         self.assertEqual(channel.count("block_collide(f);"), 1)
-        self.assertNotIn("collide_mrt_unforced(f);", channel)
+        for text in ("collide_mrt_unforced", "collide_dispatch(", "d_params.fx", "d_params.fy"):
+            self.assertNotIn(text, channel + "\n" + block_collision)
         for source in (blocks,):
             self.assertIn("(COLLISION_MODEL != 0 && COLLISION_MODEL != 2)", source)
             self.assertIn("USE_LES", source)
             self.assertIn("STORE_PRECISION != 0", source)
             self.assertIn('#if COLLISION_MODEL == 2\n#include "operators/collision_mrt.cuh"\n#endif', source)
-        # One shared unforced MRT body; each blocked/patch path calls it exactly once.
-        mrt = (KERNELS / "operators/collision_mrt.cuh").read_text()
-        self.assertEqual(mrt.count("void collide_mrt_unforced("), 1)
-        for source in (blocks + "\n" + block_collision, channel + "\n" + block_collision):
-            self.assertEqual(source.count("collide_mrt_unforced(f);"), 1)
-            self.assertNotIn("collide_mrt_no_force(", source)
-            self.assertNotIn("compute_rho_u(f, rho, ux, uy);\n            collide_mrt", source)
-            self.assertNotRegex(source, r"compute_rho_u\(f, rho, ux, uy\);\s*collide_mrt")
+        # One unforced MRT call, in block_collide only; the steps never collide directly.
+        self.assertEqual(block_collision.count("collide_mrt_no_force(f, rho, ux, uy, omega);"), 1)
+        self.assertEqual(block_collision.count("compute_rho_u(f, rho, ux, uy);"), 1)
+        self.assertEqual(block_collision.count("fmaxf(OMEGA_COLLISION_MIN, d_params.omega)"), 1)
+        for source in (blocks, channel):
+            self.assertNotIn("collide_mrt", source)
+            self.assertNotIn("collide_srt", source)
 
 
 if __name__ == "__main__": unittest.main()