Oh my goodness, roost fights are a nightly routine around here. By the way, I've noticed that when one is crawling under the other what they are really doing is trying to knock that bird off the roost. I referee the fights most every night, unless I'm in a big hurry and have to let them sort it out themselves. My half blind hen Lil' Bit waits by the door for me to put her on a roost each night (her peripheral vision sucks). I always put her right next to my roo for protection. I let my lowest ranking member roost on the cross bar between the nestboxes so she won't be harrassed too much.
My roo will break up hen fights during the day - I'm talking knock down, drag out fights - but at night he just tries to stay out of the way of all the mayhem.