Great questions !
Well my answer is that it all depends ... if you have a nice run and let out the coop into a run each and every day (or free range or have a netted area) then you can squeeze even more in a small one. If they have to EVER spend a whole day in that coop - then you are at about maximum now. I squish - or rather they squish themselves - into the large coop each night and seem very happy to be all squashed - but I let them out nearly at first light and come out once it is dark and close the door for safety's sake.
Hope that answer helped !