"Bullying" - I think??

[FarmerLisa63]

Last year I thought I had an issue with "bullying" (Backstory: chickens plucking feathers from each other out of boredom; as it turns out, because my run area was, in fact, not big enough, and I've since expanded it for them to visit for a couple hours at the end of every day, supervised, since it's not covered and we have hawks!). Increasing the run area MOSTLY rectified the issue. Everyone but two of my hens have grown back beautiful, silky feathers for the unusually cold weather we're having in coastal North Carolina.
ANYWAY, I still have these two hens who have bareness - one on her back and the other at the tail area. Nearly every day I go out for some chicken task I can see that the other hens have pulled out a feather or 2, leaving a small, bloody injury. A couple of nights recently I've gone out to spray with BlueKot on those hens injuries, in an effort to offer healing and hopefully deter the trouble makers from doing more damage.
Any suggestions for the situation are appreciated.

 

[nuthatched]

Do you have any roosters? What's their diet?

 

[Seaslug]

Are you certain that the hens are not doing it while they roost? Are they in a prefab coop? Often the roosts in prefabs are too close together and permit standard size chickens to pull feathers.