Critical subwoofer tip

I assume that everyone already knows the importance of phase matching a sub to the main speakers but it’s a little more complicated than simple 90 degrees or 180. The B&W sub that I have has four choices. In every case there has been a definite correct position that can be non standard. My current setup shined at 270 degrees vs the std positions. It’s completely obvious and the other choices would not have been satisfying. 
From my lengthy experience I would want a subwoofer with several phase choices. I personally don’t see how one could seamlessly integrate the mains and the sub without this flexibility. No one asked but i thought this info might be useful to anyone purchasing a subwoofer. YMMV
The OP reminds me why I have completely given up trying to help people get good bass in a room.  Subs are hard to configure.  Get a preamp or receiver with ARC if you get a sub.


OP is specifically commenting about setting up Phase.

With the subs I have, this was the easiest part of the whole process.

Reverse cables on main speakers.
Play sine wave file with same frequency as subwoofer crossover (ie 50Hz). Turn volume up until SPL is 0db with SPL meter set to something like 80db.
Turn sub phase from 0 to 180 degrees one step at a time and the lowest db on SPL meter is the correct phase. I assume if there is a switch 0-180 you would just flip the switch and see which one has the lowest db.
Reverse main speaker cables back to correct position.
Just to be clear, you adjust the sub phase for your seating position, not the same phase as your loudspeaker but I'm guessing it's near the same thing. Unless you are sitting at a null point. Then the sub phase will be different than your loudspeaker. Agree?  
I spent over a month getting my pair of t7i's to even sound like they managed any semblance to bass response. I can assure you if they are completely out of phase with your mains it does make a difference! You want those subs pushing out and contracting at the same time your mains are. I know there's better terminology but I'm listening to Clapton while responding. It was a pain to get it right by ear but you'll be rewarded when you do. If phase wasn't important why would we have the ability to set them? why would there be mfgs designing then with servo auto driven phase adjustments? When I did what REL said and heard when it was audibly louder it was in phase and when you listen again from LP you'll know it. Still fine tuning but getting there and loving the ride!