It definitely improved your 200 Hz response. Still got that nasty resonance at 55 Hz or so. 1/4 Wave for that is about 5', full wave is 20'. You mentioned a 20' deep room. It looks like you may need some absorption to break up that standing wave.
To me, that resonance would sound more objectionable than the lower bass output.
But that being said, 8dB is pretty low for the bass. I would say, the speaker designer might have counted on some room gain to boost the bottom end, but if these are nearfield monitors, that wouldn't have been the case.