I will chime in here with some different ideas than the ones already mentioned. Birds often peck to establish the pecking order. Now usually just a threat of a peck, and the lower bird will leave the dominant bird, and get out of sight. Think of it as curtseying to the queen. I have seen the lower bird, leave, get out of sight, and within seconds come back stand right beside the queen and eat. It is the getting out of sight that signals that both birds agree.
If you have a big flat wide open run, there is NO place to get out of sight. So even if the lower bird moves off, she does not get out of sight, and to an aggressive bird, this can raise a red flag. It is like the lower the bird is refusing to agree with it. And often times the more aggressive bird attacks again to prove the point.
So if you add a couple of hideouts, it can really help. A pallet up on saw horses, so birds can get under or on top of it. A pallet leaned up against a wall, or even a small wall standing up in the middle of the run. These are good places to set up some extra feed stations where a lower bird can eat without drawing the attention of other birds.
Mrs K