I guess I may have kind of gone off on a tangent on the floor bounce thing, but we were talking about measurements and it is one of the things I noticed about line arrays. They don't have a distinct floor bounce notch even when standing upright because of multiple path lengths from driver(s) to floor to microphone. So I was thinking out loud that ground plane measurements probably make more difference in the response graphs of point source speakers than they do of line arrays.

I like the idea of multiple subs for a similar reason, smoothing room modes.