The only real way to validate what your are hearing is to do a room response. there could be some suckout that the full range of the sub is complementing, or you might find that there is a huge hump in the upper mass response that you like, but you could refine the crossover and level once you know exactly what it is doing.
Sub best at high crossover?
I am wondering, is my ears deceiving me, or is the Velodyne DD-18 actually sounding better, when I defeat the crossover (by setting it to max, 199hz), and turn the volume some steps down? This is in a fairly large room, with the sub well positioned, augmenting full range speakers. I hope others will share experience.