I don't profess to know the "real" answer.... but here's my thoughts.
Bottome line, they (Klipsch) target "even coverage" (or maybe some other fancy term for same thing)
Rather than a narrow beam of focused sound at 100 db's at my seating position, the larger speakers disperse the sound better such that it's more of a wall of sound coming out of the speaker.
In other words, while listening to the Heresy's, once you get out of the point of focus, the sound dropps off (the scale dies). With the larger speakers, you get that same 100 db's at more points in the room, therefore the scale is/seems larger.
I might add this sense of scale does not mean LOUD.... it is there at normal volumes as well. This suggests to me that if you had an electrostatic, horn, ported... speaker that had similar COVERAGE characteristics, that you might get better scale with all of them.
That's my layman understanding....... it all begins with the coverage angles of the speakers.
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