If it's any help, I've been in the middle of a flock several times as it was flying down. Do they pitch down uphill or downhill? The answer is yes and it depends. I have mostly ridges and ravines on my place. When I've watched my turkeys fly down, they pick the downhill side if they're trying to get away from the roost. They pick the uphill side if they want to stay close to the roost tree.
I had a flock of turkeys that liked to roost on the shooting rail of one of my ladder stands. I never knew if they were there until I was almost at the top. It was amazing how long these birds would hold before busting. Most of the birds would bust downhill, because that gave them the longest distance to get away from the roost tree. I'd assume my spot, bring up my bow and wait for dawn.
There were turkeys scattered on neighboring trees as well. These would eventually wake up to the fact there was a human in their midst and pitch down. They would go in all directions, but it appeared to me that the dominant birds would fly down uphill and then start making assembly calls. The birds further down the hill would then come up. This forming up process might take the better part of an hour, and there would be some intense arguing. The dominant hens would squawk back and forth trying to figure out who was going to form up on whom. Eventually the whole crew would muster at some point up the hill from the roost and walk off feeding.
I have had similar experiences watching birds in the pre-season. In late winter, I'll have big flocks consolidate and hang out in the same ravine we call Hootin' Holler. These birds will roost up and down the creek in the tallest trees, usually a third to a half way up the hill. Birds pitch down in all directions, but they end up usually move to the uphill side of the roost no matter what.