Is there a posting somewhere that states what size bases we should be using for any given model? All I've found in the main rules are references to using that base as a frame of reference for targeting, but nothing about what size they should be.
Yes: fair point, indeed. That actually is a matter of model size, instead of the OP's question about base size. Using a model the size of a goblin makes about as much sense as using a nickel for the proxied Boss model. That probably should have gone to an all player consensus, or a roll-off to decide the validity of the model represented. Base size is one of those petty little uber-nits that the hard-core Jee Dubyeh tournament neckbeards love to pick (to the great annoyance of us casual gamers).