You should be ok. All 3 fronts will exhibit the same off axis response vertically. Seamless and superb for your second row. wink So long as there is line of sight to the tweeters (the narrowest dispersion frequencies) you should be just fine.

Its cool you are really thinking into it at this level of detail. Acoustic shadows and stuff. What I am concerned with is my wife will want to pick seating with high backs, obscuring the rear surrounds (towers on the floor) in my planned setup.... this is a bigger issue for most setups I would guess.