I actually have 1 rooster and a cockerel that knows his place. The rooster tolerates him. He is probably 18 weeks old.Likely a Dominance thing, especially if you don't have a rooster to fill in the role. There is an article on here I think. Its an interesting read.
The one on bottom just got down raising babies. So I can see that. She is probably bottom of the pecking order. The one on top maybe middle of the pack by my food and mating observation but I’m no chickenologist. Just a watcher.Maybe not real common but not uncommon between hens. It is about dominance. Most of that behavior with juveniles is not about fertilizing eggs, it's dominance related. The one on bottom is accepting the dominance of the one on top, whether by choice or by force. Whether boy or girl.