Create random number (1-6) of objects from USD using rep.create.from_usd()

Can you give omni.replicator.core.randomizer.instantiate a try? I believe the distribution should work with the size var.

https://docs.omniverse.nvidia.com/py/replicator/1.11.8/source/extensions/omni.replicator.core/docs/API.html#omni.replicator.core.randomizer.instantiate