I had a similar problem with my big bossy Delaware hen pushing and pecking everyone else off the roost. The other side of the roost always looked better to her, especially if 5 hens were between her and that end. Every evening there would be so much noise from the hen house that I would have to run outside and break it all up. It wasn't only Dolly making all the commotion- the others definitely had issues with whom they could or couldn't sit next to. So, after a lot of frazzled nerves, I decided to stick a piece of plywood halfway along the perch dividing it into half- so then there were two sections with four walls to sit against. This helped a lot. But, there was still a lot of jumping up and jumping down and pecking and pushing and shoving. Finally, in desperation, I stuck in another short perch and now the bossy girl can be by herself in her favorite corner and the other hens huddle together onto the new perch.
Most of my chickens seem to like to be on the inside edge against a wall- must feel safer- so see if you can add to, rearrange or divide your perches to give more wall space.