The problem is that 2x the distance = 4x the wire length. Losses due to wire resistance can add up quick. That said you will probably be ok based on Rachio’s internal tests:
Using 16 gauge wire on a 400 foot run (800 feet total for 2 conductors) should be no problem. I replied in another post my current readings and voltage drop over the 800 feet and it was only about a loss of a little over 1 volt. see: Size zone wiring This was using Orbit sprinkler valves