diff --git a/scripts/cache_aware_proxy.py b/scripts/cache_aware_proxy.py
index 64f2a0d..497fa69 100644
--- a/scripts/cache_aware_proxy.py
+++ b/scripts/cache_aware_proxy.py
@@ -531,7 +531,7 @@ async def _handle_combined(api, req_data, token_ids, input_length, session_id, h
     def _instance_cost(i: int) -> tuple[float, bool]:
         """Expected latency if this request goes to instance i."""
         inst = combined_instances[i]
-        queue = inst.pending_prefill_tokens / throughput
+        queue = (inst.pending_prefill_tokens + inst.ongoing_decode_tokens) / throughput
         local_hit = cache_hits[i]
         local_new = max(0, input_length - local_hit)
         local_cost = queue + local_new / throughput
@@ -545,18 +545,24 @@ async def _handle_combined(api, req_data, token_ids, input_length, session_id, h
         return local_cost, False
 
     # Session affinity: prefer the last-used instance if its cost is reasonable
+    avg_load = max(sum(i.ongoing_tokens for i in combined_instances) / len(combined_instances), 1.0)
     affinity_idx = session_affinity_combined.get(session_id) if session_id else None
     if affinity_idx is not None and affinity_idx < len(combined_instances):
-        affinity_cost, affinity_push = _instance_cost(affinity_idx)
-        # Compare with the globally best option
-        all_costs = [_instance_cost(i) for i in range(len(combined_instances))]
-        global_best_cost = min(c for c, _ in all_costs)
-        # Use affinity if it's within 2x of the best option
-        if affinity_cost <= global_best_cost * SETTINGS.overload_factor:
-            best_idx = affinity_idx
-            best_cost = affinity_cost
-            best_needs_push = affinity_push
+        affinity_inst = combined_instances[affinity_idx]
+        # Hard gate: break affinity if instance is overloaded regardless of cache
+        if affinity_inst.ongoing_tokens <= avg_load * SETTINGS.overload_factor:
+            affinity_cost, affinity_push = _instance_cost(affinity_idx)
+            all_costs = [_instance_cost(i) for i in range(len(combined_instances))]
+            global_best_cost = min(c for c, _ in all_costs)
+            if affinity_cost <= global_best_cost * SETTINGS.overload_factor:
+                best_idx = affinity_idx
+                best_cost = affinity_cost
+                best_needs_push = affinity_push
+            else:
+                best_idx = min(range(len(combined_instances)), key=lambda i: all_costs[i][0])
+                best_cost, best_needs_push = all_costs[best_idx]
         else:
+            all_costs = [_instance_cost(i) for i in range(len(combined_instances))]
             best_idx = min(range(len(combined_instances)), key=lambda i: all_costs[i][0])
             best_cost, best_needs_push = all_costs[best_idx]
     else: