The servo control on woofers so equipped can be working to absolute perfection, but it still won't address the asymmetrical radiation the typical driver has. The only way to address that system issue (should you choose to) is to add a second driver with the opposite orientation.
I know we are really splitting hairs here, but would this attribute inherent in typical drivers make one of these subs with all drivers facing front a system with a slightly cardioid radiation pattern (given that the depths of both sides of the H-frame are the same and everything else is equal and or symmetrical) rather than textbook dipole pattern? This would account for the perceived increase in bass energy Jay reported in difference between the two setups as this setup would then fire just a wee bit more forward than back with all drivers facing front?
This then begs the question (for those OCD about the looks of the system, which is where I think the idea of facing all to the front started way back when?), could one reduce the cavity depth at the front ever so slightly to decrease/reshape the output from an all drivers front facing arrangement to restore the driver radiation pattern to that of a reversed driver setup, more representative of a textbook symmetrical dipole, thus giving those who like the all drivers front look the best of both worlds?
Also, if one were trying to maintain the nth-degree of symmetry in the radiation pattern, wouldn't one need to make these subs in multiples of two drivers per stack, as a triple would only be able to reverse one of three drivers and thus still end up with a similar situation to a dual with both facing front where the output to the back is less than that out the front?
Again, please, for any reading don't think that I'm trying to contrive some sort of "night and day" kind of discussion out of the asking; this really is splitting fine hairs on what is still arguably (IMHO) one of if not the bass system audiophiles can put in their homes by which all others should be compared.