Using Shelly Uni to make Taco zone control smart

I’m trying to add a Shelly Uni to a Taco 3 zone controller, Zone Valve Controls | . I believe I can power the Shelly from the AC24v lugs. My question is regarding monitoring the 3 zone outputs. Given that the ground of the 24v should be the same as GND on the zone outputs, can IN1 and IN2 be wired directly to the +24v of the zone outputs? Wiring Shelly instructions show R1 on IN2, but I don’t understand why it’s different than IN1. Lastly, is it possible to somehow monitor for 24V on the 3rd zone using ADC_IN, while still using IN1 and IN2 for monitoring 24V AC from the first 2 zones.