Do you feel like you exhausted all of the parameters in Flex to be sure they weren't set such that your bushes weren't being watered as frequently and deeply as they should have been? I mention it because I had the same problem when I first tried Flex, but as I dove in I found that there were many variables that could create an issue with underwatering. I'm not intending to argue that your decision was not right for you, but I also don't want to leave other people looking at this thread with the impression Flex can't be made to work in New Mexico or any other state.
The cool thing about the Rachio implementation is that it's based on equations and practices that have been a standard in the agricultural industry for years. As long as you have an idea of your plant's root depth, water needs, soil type, etc., the equations will efficiently deliver water to your vegetation and keep it healthy. Get one or two of those key parameters wrong, and you very well may see the underwatering issue you described.
FYI, I found this interesting New Mexico irrigation reference. Head down to the section 'Drip irrigation requirement'. You'll see terms like Kc, ET, etc., which are all a part of the Flex calculations. The study is from New Mexico state, and the drip irrigation has data from the Farmington area.
Again, there's nothing wrong with going the route of setting a fixed schedule if you don't have the time or inclination to go with Flex. I just want folks to know that if they'd like a hands-off scheduler that operates at max. efficiency and keeps your vegetation happy, it is possible with Flex, regardless of whether or not you're in a high-desert climate. The only limitation I've seen so far is for zones that need to be watered more than once a day, and I haven't seen mention of that on this thread.
BTW @davidsantafe, I agree that if you're concerned about being 10 miles from a reliable weather station that could be an issue. Should you ever experiment with Flex again you can see that in the zone's 'moisture table'. It will show you how many inches of water were reported, and if it didn't match with what fell in your area you'd have your answer. I'm sure that remote areas without a reliable weather station nearby would be a challenge for Flex implementation. You can always get a personal weather station for your property, but that's another investment in time and money to work out.