I never thought of it before, but the birds are probably going to be better off huddling together, for warmth, during winter. We have two roosts, in a ladder configuration, about 30" wide. The plan was for 3 of our 6 birds to be on each roost, but the hens decided the lower roost is just not high enough, so they all find spots as far up as they can go.
After reading this post, I have an idea of something I can do to improve the roost...proof that your coop is never "really" done!