If your AVR sets the main's XO to "large", it means Audyssey reported the speakers roll off at below 40 Hz, that's why it you leave it at that, your XO for the mains will be "full band" as shown in my screen shots. That also means the sub won't be helping the speakers set to "large", and will therefore take care of the signal in the LFE channel only, unless you change the "bass" setting on the menu from LFE to LFE+Main (the so called double bass setting).
You are right, that practically means nothing because most people should change them to small anyway, and only then you can experiment with different XO settings, by manually adjust them to 60, 80, 90 Hz etc., until you like the bass sounding the best to you at you main seat.
I changed my main's XOs for the mains, center, surr, surr back to 80,90,60,40Hz respectively. That gives me the flattest response for both 2.1 and 7.1.