They like to huddle in corners and such, I think it makes them feel protected and safe. If you're concerned about the ones on the bottom getting crushed you could try making a three sided box for them from scrap plywood that is a bit larger then their current favorite spot and then put it where they like to huddle now.....chooks can be strange though so there's no telling if they'll use it or just find another tiny space to cram themselves into.
