I would use the Greedy allocator rather than RoundRobin. Greedy doesn’t do anything to explicitly minimize inter-chip communication, but it typically ends up with lower inter-chip communication than RoundRobin.
We also have some new allocators that explicitly minimize the inter-chip communication: GreedyComms and PartitionComms. They’re in this PR. PartitionComms is the most effective, but does require that you install nxmetis. Often, it’s the inter-chip communication that makes networks slow, so reducing that could help considerably.