Mine are currently in glass tanks, though I'd like to upgrade to some sort of homemade vision enclosure in the future. One tank is above the other three, containing my finicky, sensitive little BRB. The rest are beside each other and don't seem to mind. I actually just took some pictures of my BRB noticing my big BP in the tank below him for the first time while I was holding him. Neither seemed to have any sort of stress, upset, or aggression response. Just inquisitive.
My new yearling corn is between the big BP and the baby BP. Baby BP is unfazed by anything. Hasn't even been home a week, handles like a dream, and regularly goes exploring. The big BP is super easy going, but now that I'm thinking about this, I'll have to try rearranging a bit to see if that makes any difference in the behavior or activity level of my corn. She hasn't even been home two weeks and hasn't been very active. Might just still be getting settled, but it couldn't hurt to try giving her more privacy.
Here's a picture of my current, if not totally ideal, setup. I got the corn and the baby BP within the last two weeks, relatively unplanned. I don't like how messy the whole thing looks, so I'll be trying to figure something else out soon anyway.