Delay and phase in reference to a subwoofer are the same thing. Delay in this instance is the more accurate description of what the control is performing.
You have an unconventional listening space which may require an unconventional solution. Try what ever you can think of and see what happens. Aim your subs in different directions, Raise them off the floor, Raise them off the floor at different heights to each other, change the low pass filter setting (crossover point). There could be some cancelation caused by the interaction with the woofer in your mains. Try asymmetrical crossover points. If your speakers have ports try plugging and unplugging in various combinations. I'm sure there are other things you can try all you can do is see what happens.
In my system in a 14 x 10 x 9 room I have one sub sitting right next to the listening position aimed towards the main speakers and another sub almost directly behind that sub and aimed 90 degrees from it.
You have an unconventional listening space which may require an unconventional solution. Try what ever you can think of and see what happens. Aim your subs in different directions, Raise them off the floor, Raise them off the floor at different heights to each other, change the low pass filter setting (crossover point). There could be some cancelation caused by the interaction with the woofer in your mains. Try asymmetrical crossover points. If your speakers have ports try plugging and unplugging in various combinations. I'm sure there are other things you can try all you can do is see what happens.
In my system in a 14 x 10 x 9 room I have one sub sitting right next to the listening position aimed towards the main speakers and another sub almost directly behind that sub and aimed 90 degrees from it.