diff --git a/dsv4/kernels/cuda/compressor_reduce.cu b/dsv4/kernels/cuda/compressor_reduce.cu
index a6e07caf..c3749937 100644
--- a/dsv4/kernels/cuda/compressor_reduce.cu
+++ b/dsv4/kernels/cuda/compressor_reduce.cu
@@ -124,15 +124,14 @@ __global__ void csa_compress_reduce_kernel(
 
             float g = gate_proj[token_idx * kv_dim + gate_offset + c];
             float kv_val = kv_proj[token_idx * kv_dim + kv_offset + c];
-            // Position bias: same (m, 2*hd) bias added to every block
-            // Added to BOTH gate (softmax logit) and kv (content) per reference
+            // Position bias: added to gate logits (softmax Z + B) only.
+            // The paper defines compression as softmax(Z + B) then weighted sum of C.
+            // The bias must NOT be added to kv_val — that poisons compressed content.
             if (position_bias != nullptr) {
                 int pos_bias_row = (block_i > 0 && t < m) ? t : (block_i > 0 ? (t - m) : t);
                 if (pos_bias_row >= 0 && pos_bias_row < m) {
                     float pb = position_bias[pos_bias_row * kv_dim + gate_offset + c];
                     g += pb;
-                    // kv_offset matches gate_offset for CSA: both are 0 (a-stream) or hd (b-stream)
-                    kv_val += position_bias[pos_bias_row * kv_dim + kv_offset + c];
                 }
             }
             float e = expf(g - local_max[ci]);
@@ -192,12 +191,12 @@ __global__ void hca_compress_reduce_kernel(
             if (token_idx >= T) break;
             float g = gate_proj[token_idx * hd + c];
             float kv_val = kv_proj[token_idx * hd + c];
-            // Position bias: same (m, hd) bias added to every block
-            // Added to BOTH gate (softmax logit) and kv (content) per reference
+            // Position bias: added to gate logits (softmax Z + B) only.
+            // The paper defines compression as softmax(Z + B) then weighted sum of C.
+            // The bias must NOT be added to kv_val — that poisons compressed content.
             if (position_bias != nullptr && t < m) {
                 float pb = position_bias[t * hd + c];
                 g += pb;
-                kv_val += pb;
             }
             float e = expf(g - local_max);
             local_denom += e;