With most receivers, setting crossover to 60 hz and speaker size to Large means that the main speakers get all frequencies, while frequencies below 60 hz also go to the sub.

Setting to 60 Hz and Small sends everything above 60 Hz to the mains and everything below 60 Hz to the sub. Of course the filters actually roll off, so some signal above 60 goes to the sub and some signal below 60 goes to the mains.

On some receivers setting 60 Hz and Large means "Large wins, ignore the crossover frequency"

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8