Hi Mike, phase on both is set to 0 (as they are both on the front wall).
Yes, that is logical . . . but unless it's based on adjusting phase as you look at frequency response, it's probably wrong.
The sub has a crossover, which likely has some latency. The subs are on the front wall . . . are the mains on the front wall, too?
If there is any time or path-length difference between the subs and the mains, relative to the main listening position, there will be cancellation and enhancement at frequencies centered around the crossover frequency. And that will affect your response curve in a major way.
If you have not yet set phase that way, you may be able to get better -- possibly much
better -- results by doing so.
The effects of this are minimized by some audiophiles, simply because not all subs have a phase control. Bad reason! It's like the old joke about the drunk looking for his keys under the lamp post. "Where did you lose them?" "Over there -- but the light's better here."
Sorry to be a broken record. Trying to fix frequency response without optimizing phase is wasting your time.