What you are implying is interesting, to the say the least...in my room, a 90Hz crossover is very directional at times...the sub gives itself away...not sure if this is a flaw of the sub or what, the speakers don't do it as much, but I suspect that's because they are working in stereo creating an image. Don't really know, don't care. It's pretty well documented directional cuess extend below 100 Hz now, some argue below 70Hz, I can't hear that, but maybe some can.

I have enough room acoustic issues crossed over at 40-60 Hz to worry about before I go doubling or tripling that. And my subwoofer doesn't do nearly as good a job above 80 Hz as my main speakers do together to justify the decrease in performance just to phase align the center channel.
Still, I'll toy with your suggestions...we'll call it the Stuey method.

Cheers!