Thanks for your input.
As I see it, I have the following options:
1. Move all seating about 2-2.5 feet forward. This will place the null just between the seatings but my screen will be way to large for the front row then. Its already pretty big for the front row - I can make it smaller though, but I prefer the experience placed as far away from the screen as possible even though the ratio is the same as beeing placed close.
2. Insert aux subs as you mention. I tried a cheap Earthquake inwall, but it didn't say a sound below 30hz, so not usable in my situation. If I should use the Procella subs, then I should get at least the P15? The P10si is a great form factor, but to cancel the mode I assume it has to play that low with authority?
Another solution is just to accept the variance and focus on having the best sound possible at row 2. Tough choice!
JBL ScreenArray Cinema | 9.4 Surround | 136" Scope