I think it may be worth noting that harmonics that are integer multiples (1x, 2x, 3, x4, 5x), when the amplitude of all harmonics are the same (that never happens in nature), and the transient is the same in all frequencies (also never happens in nature), the resultant sound is what most people would identify as a pipe organ (or perhaps a woodwind sound. That's essentially what additive synthesis is.
I don't think any control on the Kemper would adjust this harmonic series, because the further that one moves away from the harmonic series (with integer based multiples) to inharmonic (ex. 1.1x 1.2x, 3.4x) then the sound becomes metallic white noise-ish. Like pitches white noise, where there is no fundamental.
So, to get back to the questions, what does definition do: it could possibly adjust the amplitude envelope of higher frequencies. Higher frequencies are responsible for what we perceive as transients, which then in turn help to give clarity to a sound's attack part of the envelope.
I'll have to sit and listen and play with the knob. I'm just theorizing...