@Trell So somehow, now the low-end feels and sounds like it's coming more from the middle of the soundstage.
Yesterday I did a full Audyssey calibration (see result in post above) with the Hsu having both ports open. Also applied a +3db to the low-end, my own house curve. In the end it was too much bass, so I removed it and re-uploaded the calibration to the AVR. And then today I decided to plug one of the ports on the Hsu, as that will increase low-end extension at the cost of SPL, but there was plenty of bass already anyway so I was curious how that would sound.
Currently I feel like the low-end is now more coming from the center of the soundstage instead of the left where the subwoofer is currently placed. Surprising that plugging a port can do that. Maybe the lower SPL output has less interaction with the walls which was localizing it too much. Didn't re-calibrate with the port plugged (and maybe I should, but liking the sound better so far).
Also have the two RSLs 10" subs on the way now, so I'll be comparing both in terms of subjective audio quality as well as objective measurements what sounds better.