Actually, I did this without the sub, just the front speakers. Their alignment is just as important as the sub/main interface.
I suggest you do this only with the subwoofer distance. When you start changing the speaker distances, you start manipulating the imaging, particularly the "phantom imaging" that happens between a pair of speakers. This is related to the Hass Effect, (aka the "Precednce Effect.") When two speakers are playing the same content, and they both arrive at the ears at the same time and level, they are perceived by the brain as coming from in between the two speakers. This effect is most noticeable with 2-channel systems where voices are mixed so they "image" from the middle of the two speakers. However, even in multichannel content, sounds can be phantomimaged between adjacent speaker pairs. So, you can hear sounds that image between the L and C, and between the C and R. Phantom images can even exist between the fronts and surrounds or between the sides and rears.
If you change the arrival times of the speakers, you throw off these effects. The sounds that arrive earlier takes "precedence", and becomes the predominat sounds. The brain perceives these sounds as coming from the direction of the earlier arriving speaker. In the case of voices mixed to be in the center, the image will collapse to sounding like it is originating at the earlier arriving speaker.
If you instead keep the speakers all at their optimal distances, and manipulate the subwoofer distance, you can keep the proper imaging of the speakers while still getting the sub properly timed with all the speakers.
When you manipulate the speaker distance to optimize the bass response you potentially compromise the imaging. Better to manipulate the subwoofer distance. This has the same effect on the bass response with no impact on the imaging.
Good luck and I hope this helps.
Craig