PS: I got a memo from all the older birds. It said they all wanted their own personal roost to themselves...at least 8 ft long each.
That's not ONE for the 6 older girls. That's 6 roosts...each one 8 ft. long. They started picketing and the next step is to go on strike from laying eggs.
I could see them developing a habit like this over winter, if they spent a lot of time indoors. Without as much to occupy themselves, they may have taken to fussing and fighting over roosts.
There's a really good correlation with human behavior. If a group of people live in a subsistence agrarian culture, the things they'll fuss each other over will have to do with the demands of that lifestyle - land ownership, pasturing rights, fair prices for seed and grain at market, horse trading and the like. If a group of people live in suburban America where appearances are paramount, the value structure radically changes. People fuss their neighbors about the length of their grass, and whose tree branches are overhanging whose fence. People today will kill each other for shoes. A hundred and fifty years ago a lot of people didn't bother with shoes.
So if the analogy holds true - and it might not; I could be totally wrong about all this - then when chickens are outside a lot, they may try to snatch bugs away from each other, or chase each other off of patches of tasty weeds, or whatever they think is important outside. When they're confined to being indoors, all they have to fight over is the roost. So the top chicken is
by God going to have the best roost! And there may be no difference at all between one spot and another, except that the chickens arbitrarily decided it is so.
Actually, it's a lot like American Politics.
Anyway, now that they've got the habit of fighting for roost space, they may be carrying on with it, even thought they can get out more, just because it's habit. I suggest three possible courses of treatment.
1 - Re-arrange the roosts. Move it/them to a totally different location and height. Ideally, install several at different heights and multiple corners. I have no idea how feasible that is in your coop.
2 - Lots of enrichment outdoors. Put some cat toys out there, add a new dust bath. Give them something to think about besides the roost. Do this in addition to #1 if possible.
3 - Lock them out of the coop at about an hour before they usually start fighting. Keep the door closed until they're just about to sleep on the ground, then open the door and let them go inside. They may be too tired to fight, and will just pick a spot to go to sleep.
Keep in mind that all of my advice is
totally baseless and there's a better than fair chance that I'm completely wrong. But hey, even if I am, doing some of this stuff will give you a false sense of control over your life, which most people find quite uplifting, while it lasts. ;-)