Actually the main reason for the horizontal position is for it to fit better on top or below the TV as vertical speakers are harder to place. Hutzal has 2 vertical M2s and he loves them. The best sound would be 3 of the same speakers across the front.

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70