@jleh That’s interesting info. I’m not an expert, so I’m not 100% sure if it’s valid to use 6", or something deeper. I think 60" is somewhat standard for the agriculture industry based on this article.
This is the comment that I keyed in on that leads me to believe that one should try to match the root depth in their zone of interest.
“Available water capacity is often stated for a common depth of rooting (where 80 percent of the roots occur). This depth is at 60 inches or more in areas of the western United States that are irrigated and at 40 inches in the higher rainfall areas of the eastern United States.”
My guess is that you’re close enough for your lawn. I would use the settings that you’re comfortable with here and, understanding the range of AWC that you have underneath, keep an eye on runoff. If you are watering too often you may see runoff, and that might lead you to try a slightly higher AWC. If your soil gets significantly dry between watering maybe you need to drop it a tad.
For your other zones, consider the same analysis. If you have trees and shrubs the roots will go much deeper, so you should likely change the AWC for those areas to match the deeper root depth. Thanks for asking these questions, it gets me thinking, researching, and above all learning!