Two Channel is Better, if Vertical Mono

I have two M60 Professional Monitor NHT speakers powered and equalized by an Xda (amp, electronic equalizer and more), mounted one above and one below my listening position.
I also have as left and rights these same two, identically powered.

And when I play J. Cash, in 'Cash', 'American Recording', then what sounds best, in this mono recording? Selecting speakers left and right horizontally in the 'stereo' mode, or above and below in a 'vertical' mode?

The vertical array blows away the horizontal in stereo. NO COMPETITION. He is there, Cash, positioned precisely right in the middle, and no smearing.

It's as Floyd Toole's measurement's suggested it would be; avoid comb f. in horizontal arrays (vertical, no problem, hmmmmm)!
Good for you, you tried something and it worked out. Now if everyone would just experiment a little......
Are you essentially playing a mono recording through a single speaker that is made up of two vertically aligned speakers? If so, I would expect this to be the case, but also that the majority wouldn't have the capability to setup for both options. Since most music is at least stereo in nature I'd expect a horizontal seperation to sound much better on the majority of recordings.