OK, that helps. So, you have 16 total feet of roost space for 31 chickens. Because they're only 10 to 6 weeks old, they're probably not full grown so you probably currently have enough space. Will you keep all 31 chickens or are some roosters which you'll make for the dinner table or give away? If you'll have 31 chickens ongoing, it would seem you *might* be tight in the future based on the guideline of 8 to 10 inches per chicken of roost space. This is just a guideline, however. But I suppose when you get to that point, you can deal with it then if it becomes an issue. Maybe someone with more chickens can comment as I don't have experience with this many chickens.
I would suggest not putting the ones who do not get up on the roost on their own up there. If they're not ready, it'll be just that much harder on them. They'll get up there when they're ready. 3 feet off the ground is not high at all so even the 6 week old chicks can get up there if they want. If you doubt, worry about this, given them a little step to hop on below and in front of the roost. In the mean time until they're ready, let them sleep together on the ground, the ones who want to do it that way.
There's not much else you can do that I know of, based on what I've read and experienced, that you haven't already done, to avoid having them pile on each other. You have 2 roosts so those that are being roughed up on the roost can choose to use the other one. And you put them both at the same height but it sounds like there is a preference for one over the other? In my (albeit limited) experience, the ones who get too roughed up eventually choose to roost elsewhere and you've given them that option with your second roost. In my case, I have a small group of chicks who roost on the other side of the roost (the right side in my picture) as I guess they finally decided it's not worth it to fight the others for the "prime" roost space. Why any particular piece of roost board is considered prime, only the chickens understand.
Guppy