Nuetron sensitivity and distortion

[gorohon]

I can't seem to get this thing to sweep on higher notes easily.  I have to crank the "Gain" knob on the "up" mode to get it to sweep sometimes.  I always get distortion in the range where my playing style effects the envelope control.  I have messed around with "Rx" and notice that lower values favor the "Down" mode and higher values closer to 4.7k favor the "up" mode.  But, I still have distortion!  Everything else seems to be working fine.

I'm just wondering, how I can get more sensitivity without distortion?