I guess I forgot to put the Your Mileage May Vary disclaimer! 
I just hooked up a PS1 unit I had and with a Z-4000 (pure sine output) watched the Volt and Amp meters as I adjusted the throttle handle. The Z-4000 "starts" at about 7V and I could hear the fan motor start but clearly not to speed. The fan reached a constant speed at around 10V (based on listening to the whirring sound). Smoke started between 8-9V. At about 12V, the smoke production was prodigious. Since your interest is in lowering smoke volume, I didn't mess around at higher voltages and focused around voltages below that.
When I enabled the jumper, the Amp reading on the Z-4000 dropped so the power into the heaters is definitely being cut. Then, with the jumper installed, I could alter smoke volume from 0 smoke at 7V to a little smoke around 9V to much smoke at 12V. Yes, I realize "little" and "much" are not technical but the point I was able to smoothly adjust the smoke volume over a range.
Something curious happens when you enable the jumper. You can hear the fan motor speed up! In other words, at low track voltages when you cut the heater power, more voltage is made available to the DC motor regulator chip and the fan spins faster. In other words, by cutting back on heater power, more voltage is made available to the fan. This has to do with the AC-to-DC conversion as the heater resistor(s) and fan motor are driven by "pulsing" 60 Hz voltage.
Finally, to peel another layer of the onion. This is somewhat counter-intuitive but the way the circuit cuts power to the heater resistor (when the jumper is enabled) is by inserting both heater resistors into the circuit...but in series. This doubles the resistance so the actual power drops. I bring this up because how you install the wicks in the chamber affects airflow since smoke is effectively "produced" where the wicks touch the heater resistors.
As previously mentioned, a chopped-sine voltage is processed differently by this circuit. The objective here is to control your PS1 smoke unit ... not to devolve into technical mumbo jumbo.
Bottom line. In my sample-of-one experiment, the jumper indeed lowered heater power at low track voltages. The smoke volume was adjustable by changing applied AC track voltage.
