"If you add tree stumps and other places to perch, having places to retreat can help." Azygous good advice
Many times the run is an open, bare rectangle. Setting up a pallet on bricks, leaning one up against a wall, creating a small wall in the middle of the run, adding roosts to the run, can give birds a place to get away and out of sight of other birds. It may make things look cluttered, but it actually increases the square footage of the run as birds can be at different levels.
But generally speaking, when you have birds raised up together, and then one or more becomes the bully, as the birds have gotten bigger, and the space remains the same, the less space they have. What is your count, what is the space? Often times, you need to reduce the size of the flock to make them fit better. Almost always, tension in the flock is due to a lack of sufficient space.