What is the determining factor to selecting the crossover point? Currently I have e speakers with built in subwoofer amp with the crossover set at 40. The woofers are 12” and the mids are 5.25”. Does one really want everything below 40 going to the sub or is a better crossover point 100? Or is the setting more a personal thing to compensate for all other listening variables?

Also, when is it best to set your speakers to large or small, given a sub is in your overall setup?

I am just trying to understand some of the intricacies/subtleties of speaker and amp set up.