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 coop, leave them alone 5-10 min, go back to check and they'd all be inside, I'd shut the door and turn off the light.  This was far better than me on my hands and knees chasing them each night to put them to bed.  I no longer have to do this.  They put themselves to roost without a night light.  I maybe used the light for a month.  You could even use a battery powered flash light or something.  It's just temporary.  Also a second roost at the same height might help, some of my girls like each other better than others, this allows them to spread out if they are annoyed with each other.  I usually find mine split into two groups, not always the same birds in each group.