Ok, I just spent the whole time driving home thinking about this, and I still have yet to figure out how that is a better way to wire them up lol. Not trying to argue, and if you don't want kind of a debate in here, just tell me and I'll shut up lol. But I feel like we can get some good info out there by maybe going back and forth with ideas.
So anyway, here's my theory. And I'm mecp certified and this is the way that the mecp standard says is correct. Basically take out of the equation the two boxes the subs are installed in. Since they aren't connected together at any point what happens in one box doesn't affect what happens in the other. Look at the whole interior of the truck as the enclosure, since this is where the two subs are affecting each other.
Basically, bass is all about pressure. Now, if the subs are wired in phase, they both are doing the same thing at the same time. When they both hit, they push in on the enclosure (interior) at the same time, obviously creating pressure, not absorbing each others pressure, but essentially pushing on each other. When they are playing out of phase, when one come is moving out, the other is moving in, essentially canceling out any pressure wave created. For example, if the sub on the left moves out and displaces 1 cubic foot of air (just for the example), at the exact same time, sub on the right moves in and creates one cubic foot of airspace. Pretty much acting like a sponge and absorbing the pressure waves from the opposite subwoofer.
The only time I can see it making sense to wire subs out of phase in your situation, is if you had one subwoofer facing cone side out, and one facing magnet side out. This theory is the same whether it be subs, door speakers, or tweeters, opposing frequencies being created at the same time in the same airspace absorb each other. This is why you never hear of door speakers being wired out of phase, it's essentially the same situation. Mecp makes it clear that you NEVER want to do this lol.
Just trying to get some constructive conversation out there, not trying to argue.