My report back is only subjective and almost useless so I hestiate to post, but wanted to follow up.
Trying with LS50 Meta, 6ft from any wall (reflective walls), the imaging/depth is amazing.
Putting them 6" from the front wall, no treatment, I have lost the depth. Distance from side walls not changed.
Same setup, 6" from the front wall, adding 3" foam absorbers directly behind the speakers, maybe a foot coverage on either side, and above and below, behind each speaker, (probably not nearly physically wide enough to cover the 360 degree radiation at 400hz and down) this did not bring the imaging back.
I really wanted to ignore the subjective reports of loss of imaging, but I felt it too. Yes yes yes, not double blind etc.
It occurred to me that Genelec might be expecting more nearfield users. If the extra "imaging/depth" would not be found in a treated room anyway at distances where direct sound dominates (assuming the depth perception is due to reflections), then nothing is really lost.
If I ever get around to treating a much larger area or an entire wall I will try this again.