That’s what I tried originally. I tried it again today, but it only works when the dumb switch is in one position. I changed the Neutral & Switch Type parameters several times, but no combination worked (including the technically correct Non-Neutral / 3-Way Toggle combination).
It turns out my wiring is more like this:
The fix was to use the GE Aux switch instead of the original dumb switch in the “left” box:
- I connected the Load (white) from the RS Dimmer to the Load going to the lights.
- The Traveller from the RS Dimmer (red) was connected to Traveler on the Aux switch
- I pigtailed the Line from the lights to the Neutral on the Aux switch.
- Changed the switch type for the RS Dimmer to 3-way momentary.
Now it all works.