Thank you for your intensive reply to my inquiry, also thank you for your visits to my posts on my project thread. I understand your various points, even though I feel the "degree of SP disappearance" would be greatly dependent on subjective demands and impressions, and it would be also greatly dependent on our room acoustics.
In any way, our interests and experiments/experiences would be highly valuable in deepening our knowledge and providing further preferable options on this issue, I believe.
Very fortunately in
my latest setup, the SP disappearance remains unchanged even if I move my head within about 0.7 m (70 cm) from the best listening position, left-and-right, up-and-down, forward-and-backward. This means both I and my wife can enjoy it sitting together side-by-side on our listening sofa.
Thank you again for your comments and discussion in detail.
Really nice setup! TAD R1s has been always one of my "dream" speakers; I once auditioned it at quite a nice audio showroom in Tokyo, and I felt the same as you are enjoying now.