I agree, with enough subs it doesn't matter where they go. In a sense, I suppose this is all academic if you use enough subs. It may be that two subs in addition to two woofers in the mains works pretty well. The more you add, the smoother response becomes. By the time you've reached three or four subs, you've reached a point of diminishing returns and it also becomes less relevant where they are placed.In Welti's study, several placement configurations were tested. A single sub was used and placed in various locations. Pairs and groups were also tested, with group sizes of 3, 4, 5 and even large groups like 10 or 20.
The results were pretty clear, that the most uniform response was obtained with large random placement, subs in each corner or subs at the midpoint of each wall. The large random group placement was found to be good, but no better than the placement in each corner or at the midpoints of each wall.
I think it is important to notice the large random placement had two unique features, one being the number of subs and the other being their random placement. In this case, I think the high number was more important than the placement because there was just so many of them.