This phenomena is definitely known by Axiom as in their blog about speaker placement of bookshelf speakers there is a section talking about putting the bookshelf speaker on it's side
If you put the speaker on its side, that now becomes the vertical dispersion of the speaker and forces what was the vertical to become the horizontal. What does that mean? You won’t get as smooth a response off-axis.)
But what they don't go into in the video is if that knowledge was used in the design of the centre channel speakers and they are constructed in such a way to overcome that phenomenon.
If I am paying over $1000 for a centre speaker to match my M80, I would like it to sound right, and not off-axis different.
