References available on real life room "tuning"?

Natural fibre fabric behind the speakers. Try thick wool carpet pieces.
Some kind of sound absorption at the first reflection point.
Nice comfy sofa to absorb sound at listening position.
If your couch is positioned against the back wall, all the better as your head is close enough to the back wall for your brain to not process reflections (it's what they do when in caves-get against a wall to eliminate echos and fix on actual sound source).
Hope this helps.

All the best,
Nonoise

I don't know about that. Due to room constraints, my head has been against the back wall for over 15 years and I get great bass reproduction. Tight, taut, and tuneful. Could it be that I also listen in the near field?

Sounds like something else is at play with your setup but mine is at the best it's been.

Doggitter, try some different footing approaches and set ups as no one thing is going to solve your problem. What is thought to be reflections can be a host of other things combining to make your listening pleasure not what it should be. I mention this because I recently experimented with some footings for my speakers and was surprised at just how much it affected the sound.

High end sibilance and other irritants can be easily judged to be due to reflections when it can be tamed by different footings, spikes and bases for your speakers.

All the best,
Nonoise

Rodman99999,
Thanks for the clarification. My speakers "only" go down to 40Hz so that probably helps as well since I'm not reproducing the really deep bass notes.

All the best,
Nonoise