There is about 18 inches of unoccupied roost to the right of me in the photo...6/7 of the girls cram together every night and then there are the 2 to 3 goof balls who roost in the nests.
We purchased the coop from a guy in Maine and it is made for up to 15 hens, it is 5x7 feet.
Your coop space is too tight especially for a cold climate. I agree with DobieLover that 9 is a little more realistic, though if you get extended periods of very cold/very nasty weather then you'd want more than just 4 sq ft per bird, as they may spend more time indoors.
For now you can block off the nest boxes at night with some cardboard or wood scrap, but you may find those birds on the floor instead. Another roost bar somewhere would also help, as it's likely these are the low ranked birds and they're getting harassed when trying to roost even though there's space left.