Well there's no telling but for the practical trying and it may be different in different stage environments. You get better dispersion with the tall stack. I used to use two one-way 15" Thiele cabs with vented ports and they were configured so that when stacked the ports were in the middle.
I believe the old Sunn 2x15 cabs where set up that way too, It cant hurt to try.
I should have about 8 solid hours of break in time on the new cab by this evening, hopefully I'll get to open the pair up a bit!