Been there, been doing that for years.
Not to derail this thread, but read the comment by IvanMike who posted that thread...
"of course you should trust your ears before anything else (i like my mixed setup better than two of either cab i own). But, the science is worth knowing, and helps explain some combinations I've tried which sounded plain weird or aweful."
Yes, the science is worth knowing.
No, it is not generically applicable to all situations.
There's no such thing as a generic 15, or a generic 10. Short of measuring each driver individually you'll never know if your phase is perfectly in tune, even identical drivers from the same manuf. can vary significantly.
Even with two drivers you've hand selected to be perfectly in phase, if you build a 2x10 with them and the listener is not perfectly on-axis they're going to have phase cancellation.
Ideally we should all be playing a single full-range point source driver (check out plasma speakers).
Short of that everything else is compromises, and there are far larger fish to fry when setting up a rig.