That's what I'd do, one bar in the middle of each. But I would not expect them to split evenly with half on one and half on the other. They seldom react the way you think is logical.
They may all try to crowd on one, short as that is. If they manage that, I'd let them. Most may crowd on one roost with one or two roosting on the edge of that tray. This is actually what I'd expect but they often prove me wrong. You never can tell for sure. If they consistently roost facing out so the poop goes in the tray I'd leave them alone.
If some sleep on the edge of the tray and face in, I'd move those to the other roost after dark to see if I could get them to sleep over their. Move at least two. It might work, it might not. If I tried moving them consistently every night for three or four weeks and they don't get the message I'd give it up as a lost cause and either live with it or remodel the roosts.
Please let us know how this works. I'd be interested in what actually happens.
