If I wanted more water in one zone, is it best to decrease the coefficient?
It depends on what you mean by ‘more water’. The zone attributes table about midway down this page shows how various settings affect watering frequency and/or watering duration.
How is your zone currently set up and what type of schedule are you using?
I believe Rachio should create a basic and professional interface. Obviously the current interface is for professionals. The basic interface should have a advanced zone setting with 2 options, max run time and a more - less water per application slider.
Before replacing my old system I knew that X min per zone was the max I needed to water every other day. I feel that during the setup it would have been great if I was asked if I wss upgrading an old system. If so, what were the max watering times per zone. Then rachio could could look at that time and the weather and guesstimate a time per zone per application. The user could then simply adjust the slider to a more or less setting. I doubt most users want to spend hours researching all the options that currently exist. People are basically lazy. They just want their new smart system to look at the weather and save them $$$ with the least amount of effort as possible.
Are you still struggling with this? Also, but more water, do you mean longer watering duration or more frequent waterings?