RUB size versus age/weight/length

[Sasha2]

I like small tubs/rubs for the little babies because its easier to find them and feed them. But 18 inches is a good size, I dont think a large tub would be a problem.
I personally think its a personality thing, I have some corns that are active and seem to like the large tubs and others that just waste the space and rarely come out to explore and just do better in the smaller ones.