Just FYI for the Rachio team, I was helping one of the members via a private chat and noticed that video I wanted to link to has potentially bad info (as far as I can tell).
The video in question is about master valve here:
The issue occurs at around 1:20 mark with instruction showing that master valve should be connected to the M terminal and SC terminal. As far as I can tell this would not work and the proper instructions would be to connect the valve to M and C terminals like you show here (link) and within your app.
I maybe missing something, but as far as I know there is a 24V AC difference between C and SC termianls, so they can’t be a substitute for each other the same way C and SP terminals can.