Have you checked the basics? Have they always been low on bass, or is it a new thing? Has anything changed?
Being in a NULL is a real thing, and almost nothing will fix that other than moving the seating spot, or speakers.
Just having gone through this myself with other speakers, it drove me nuts for months. Turns out, I swapped polarity (Rch) from my sub to main speaker. It sucked the bass out of the room. Thought there was an issue with my sub, until I setup my SPL meter, started a 40hz tone, then panned L-R on my balance. Went from good bass, little bass, no bass.
Felt like a dumb A$$, but was happy it was such an easy fix.