It would seem to me that bees would naturally be able to move up the comb better than side to side? i.e. if the ones on the bottom were to move up to the top, the whole cluster could move w/o leaving the cluster. However, side to side that's impossible. Now, do they do that? I have no clue, I'm a first year beek, but if I were a bee, that's what I'd do :-D
So, is it harder for bees to winter successfully in a horizontal based hive than a vertically based hive? That's my real question I guess.