BW, when the speaker is set "large" there is no actual "crossover"; the speaker plays full-range(limited to its ability, of course)and the sub plays none of the bass in that speaker's channel. If a special mode usually termed "plus", "double" or similar is selected(which I never do)with "large" speakers, there's still no crossover, but the sub will also play(along with the main speakers)the bass in the main channels below the selected frequency.
In contrast, with a "small" setting and 80Hz crossover the speaker is rolled off below 80Hz and the sub primarily plays those bass frequencies and is rolled off above 80Hz, the "crossover" frequency.
