In that case you are correct and I stand corrected... in general I personally prefer a larger volume as in the sofa setting, I'm more into Stereo than Home Theater and follow a conservative approach to avoid any risk of eventual overcorrection but in the case that you mention where speakers are blocked then a smaller variation as you mention would be preferable.
I am also now confused. Are you saying that for stereo measurements, the vertical spacing should be 36 inches (18 above the ear and 18 inches below the ear)? If so, the lower measurements will be taken well below the top of the back of the chair. If so, how far away from the back of the chair should the microphone be placed?
Thanks for your input.