Assigning pitch follower to pitch mix won't isolate the lowest note(s) of a chord. You might get something usable with Octave Divider type since it's more like a monophonic synth, but that can get glitchy. If octave divider on the III supports local detection, low-passing the signal around 150 Hz or lower before the pitch block might help.
Better IMO is a lowpass into fixed harmony type (dual/quad shift on the III). Local mono tracking will probably sound best most of the time, but if it glitches, try local poly.
Instead of just having an octave-down voice, you could add harmonics: first octave (original input note) by reducing mix, plus higher shifts like +7, +12, +16.
A pitch-based shutoff of the bass-simulator might still be desirable, to prevent low end noise from getting through during higher single-note playing.