Ok, looked at various LMNC schematics and the stripboard one does indeed leave it unconnected, the #1222 performance one uses proper voltage dividers (centre note is 0-12 V, fine tune is 0-1 V) and the Fartbox has a switch between GND and unconnected!? Hmm, need to go look at that PCB, I think.
EDIT: Turns out the switch is what’s called “sphnc tight/loose” on the Fartbox, or robot (
) vs. human (
) according to the video. The stripboard is a bit more sanitized, and calls it “low end on/off” which is pretty much what it does – as you move from unconnected to GND, and on to −12 V, the further down you can tune things with this control. Your choice 