The most important things I've seen in bullying between hens are to make sure they have LOTS of space, LOTS of roosts at different heights and in different spots to give themselves space and get away when needed, and multiple food and water stations so they can spread out and the bottom hen doesn't get pushed away from the food/water. Also a variety of things to do/scratch through/etc so they aren't bored and are less likely to "make" entertainment for themselves by ganging up on one. Even with all that, there are some hens that are just incorrigible bullies, or some that panic and draw more negative attention to themselves by freaking out when others approach. I have had one case where I needed to rehome the top bully into a much larger flock, where she was put in her place and behaved much better. Not sure how big your group is or how much space they have, but just things to consider. Best of luck.