Your birds are probably bigger now than when you got them, but it sounds like they have enough space. Make sure the roost bar is 12-18 inches from the coop walls and ceiling. I second the night light idea. My pullets were "scared" to go in the dark coop at night, I'd turn a light on in the...
Do your chickens currently go inside their coop to roost at night? or they never go in?
How many square feet is the coop?
How long is your roost inside the coop?