It could be the DD18 room compensation software, or maybe your power amp works happier with higher crossover point.
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.