I see that 4 sf per bird is rule of thumb for coop space. Does "cubic sf" come into play at all? Mine has 12 sf open floor space and 8 sf nest box space, but also, there are 3 staggered perches within the head room above, nearly 4 x 4 x 3. Does this space matter when calc'ing # of birds in the coop? New to chicks, thanks for the help!