Good on 'ya for trying various things and noting the differences. Measuring the frequency response / SPL (dB) is also important for trying different things so you have a record of the sound for each setup variation.
You wrote: "the biggest issues are probably 1) soundstage height is a bit too low and 2) I still want more overall bloom in the soundstage (envelopment from up down left right)."
1) Sound stage height too low: Try sitting on the floor ;) Seriously, put a rug on the floor to kill flutter echo between floor and ceiling and see if that does anything for soundstage height. Otherwise, keep the wood floor bare and raise the front of the speakers (or lower the back of the speakers) with the thinking that just as side wall 1st reflections that aren't absorbed or diffused help with widening the apparent sound source and increase listener envelopement, so too should it work in the vertical domain. Raising the front of the speaker's will put more HF energy up to the speaker and subtly call your attention to the height. However, it's not likely to be as drastic a change as lateral reflections because we hear more effectively latteraly rather than vertically due to our ear positioning on our heads. Lastly, you could add white RPG Skylines (see my system or others that use it) to gauge if this impacts the height. Personally I didn't find it added much but that could be due to my speaker's vertical dispersion pattern, or lack thereof or the sheer angle that the 1st reflection is at given I sit near field.
2) Soundstage bloom and envelopment is a funtion of indirect sound resulting from reflections from bare or diffused surfaces, and mostly from side walls which you lack. Have you considered rotating your system 90 degrees like I mentioned previously? I know it's a lot of work - ugh.
You wrote: "the biggest issues are probably 1) soundstage height is a bit too low and 2) I still want more overall bloom in the soundstage (envelopment from up down left right)."
1) Sound stage height too low: Try sitting on the floor ;) Seriously, put a rug on the floor to kill flutter echo between floor and ceiling and see if that does anything for soundstage height. Otherwise, keep the wood floor bare and raise the front of the speakers (or lower the back of the speakers) with the thinking that just as side wall 1st reflections that aren't absorbed or diffused help with widening the apparent sound source and increase listener envelopement, so too should it work in the vertical domain. Raising the front of the speaker's will put more HF energy up to the speaker and subtly call your attention to the height. However, it's not likely to be as drastic a change as lateral reflections because we hear more effectively latteraly rather than vertically due to our ear positioning on our heads. Lastly, you could add white RPG Skylines (see my system or others that use it) to gauge if this impacts the height. Personally I didn't find it added much but that could be due to my speaker's vertical dispersion pattern, or lack thereof or the sheer angle that the 1st reflection is at given I sit near field.
2) Soundstage bloom and envelopment is a funtion of indirect sound resulting from reflections from bare or diffused surfaces, and mostly from side walls which you lack. Have you considered rotating your system 90 degrees like I mentioned previously? I know it's a lot of work - ugh.