Here's what I think is going on. I believe you cannot hear the full bass range at the volume you have adjusted it. In other words, when some of the bass range is not heard what you do hear may sound delayed or detached when the reality is the front end of the bass, or its decay is just perceived absent at the volume level set. The fix is to turn up the bass at low volume and turn it down at high volume and/or adjust low pass filter to a lower crossover point to get more bass from your mains. These adjustments will make frequency response seem more seamless.