Fix AllReduce regression due to previous max range increase for LL64/LL128 (#1787)

* Adjust tuning factor impacting more than 2 nodes
* Scale max LL128 size for > 2 nodes
* Retune max LL128 range for N > 2

src/rccl_wrap.cc

@@ -52,7 +52,10 @@ void rcclUpdateCollectiveProtocol(struct ncclComm* comm, size_t const& nBytes, s
       // When LL128 is performant, the next condition overrides the previous LL choice
       if (comm->topo->ll128Enabled) {
         if (info->func == ncclFuncAllReduce) {
-          ll128Max += (log2i(comm->nNodes) - 1) * comm->minMaxLLRange[tunableIndex][NCCL_PROTO_LL128][RCCL_PROTOCOL_FACTOR_IDX];
+          if(comm->nNodes > 2) {
+            ll128Max *= 3.8; // Scale max message size for n > 2 since Tree has special behavior at 2 nodes
+          }
+          // ll128Max += (log2i(comm->nNodes) - 1) * comm->minMaxLLRange[tunableIndex][NCCL_PROTO_LL128][RCCL_PROTOCOL_FACTOR_IDX];
         }
         if (sizePerRank <= ll128Max && sizePerRank > ll128Min) {
           info->protocol = NCCL_PROTO_LL128;