No matter what various guidelines and specs may say, many problems go away when you give more space. You do not mention problems when your birds are out free ranging-- I'm thinking that's because they have so much space out there.
So in the context of birds pecking or bullying at roost time, the size of the coop IS relevant. For example, if you had twice as much coop space and twice as much roost space, there would be more options for them to spread out, and the lower ranking birds could stay further away from the higher ranking ones.
Guidelines for chicken space often assume they are are all the same age & breed. If any are different breeds, or are different ages, they tend to have problems even when they have space that seems like it should be enough. (Which is why the recommendations on this forum are often higher than you see elsewhere-- many people here have a variety of breeds and a variety of ages, so the extra space really is needed for their chickens.)
But since you say it has improved to the point of not being a problem, then I'm glad they did work it out!