Minimum settable crop coefficient in ios rachio app

It looks like the ios rachio app prevents me from setting a crop co-efficient of less than 20% while if I did it online on my desktop, it allows me. Bug, feature or PEBCAK?

I have a low water usage plant zone which is partially under shade and till I got comfortable with all the Rachio settings, I wanted to just use the crop coefficient as the sole variable to control various zones. Plus, I wanted to know what Rachio did behind the scenes with sun and shade before I did that as well.