Me too.
I've got 16 two to four day olds under a 12 x 24 right now and there's plenty of room.....the back is open for egress.
I have found the back being open makes me sleep easier. I move mine out from the edge of my pens so they can get out on two or three sides depending on which pen they are in. I do not get the distress screams I use to get now and then when the back was closed.