I'm not sure there is a consensus, but the closest thing I've found to it is that people tend to recommend 2x4, set flat side up. This way, in freezing weather, the hens can lay flat atop of their feet, thus keeping them warm. I've got mine set up so that the narrow end is up. I think it is a little more natural for their feet to grip around something. And...I believe the chickens legs are still covered by their feathers.
In all honesty, I suspect it matters more to us than the chickens. They'll roost on whatever, and I agree that they like the 5-6 feet off the ground part, with the only caveat being that they often require some help getting up to them (as they age), like a crate on it's side, or an intermediary perch.
Don't sweat it, it will be fine!
Brian