It's not just a problem with RIR. I had a hard time integrating with BRs, Welsummers, Wyandottes and Australorps. ALL of them picked on the new pullets I brought in. They just don't like newcomers.
My coop has a dirt floor. I simply put up T Posts, wrapped in chicken wire floor to ceiling to section off a portion of my coop. I'm sure you could build a frame from 2 X 4s to do the same thing. This allows the adult birds to have a 'birds-eye' view of the newcomers and a chance for them to...