Robo if a hollow tree falls over in the woods wouldn't that be pretty close to the same configuration as a top bar hive?
True, but the only feral colonies I have seen in fallen over trees have been ones that where established before the tree fell. It has also been my experience, that in general, these fallen tree colonies don't survive as long as standing tree colonies. Of course there are always exceptions.
As far as "natural" hive configuration goes... Bees will set up house keeping in any crevice that is the right size. So I don't know what natural hives are.
Bees are survivors and will do what ever they can to stay alive. If given a choice I would bet they choose a hollow standing tree over a fallen one. They will choose the best "available" cavity they can find. The best "available" doesn't necessarily correlate to a good one.
I think the barrel hive might be to big that you have comb collapse.
When left alone, I never had comb collapse with the barrel hive. The only comb collapse I have experienced has been when moving them, not just TBH, but hives with foundationless as well.