In fact this phenomena was identified some 60 years ago, and was the basis for the 'original' line arrays, the column speaker. Side by side speaker mounting was made popular primarily due to the cabinets designed by Leo Fender and Jim Marshall. Leo did not play guitar, Jim was a drummer, and neither was an audio engineer. If the original Twin Reverb had been designed by Harry Olsen instead of Leo Fender it would have had the two twelves vertically stacked.