Interesting that you went to 0.4in/hr to get the watering you need with the 2 GPH. I've figured out that mine is mostly 1 GPH single point emitters, and I had to go to 0.2 in/hr to get the watering that Water Use It Wisely recommended. I'm not in the desert, but I had been doing 130% of the time to get the watering time that it seemed the plants needed, not scientifically at all, but just based on watching them and how they responded to the water - I had started with 0.5 in/hr when I set the system up (which watered WAY too short - and I had to go to 150% to get to what the plants seemed to like better), then went down to 0.3 in/hr, and after reading through Water Use It Wisely, I'm now down to 0.2 in/hr and I've been able to remove the +/- amount and let flex daily do it's thing.
BTW, the PR = (96.25 (A*B))/C calculation made no sense to me with emitters. Assume C=1. I haven't exactly counted all my emitters, but if I go with 75 1GPH emitters, I come up with 96.25 (75*(1/60))=120 in/hr, And if I have 100 of them it's 96.25 (100*(1/60))=160 in/hr. Neither one of them puts me anywhere NEAR the 0.2 in/hr that appears to be working fairly well! So thank you to @redwagon for getting me to understand that I probably need to make C equal to the number of emitters. So even doing that, I still come up with 1.6 in/hr which would still not get me enough watering time.
Hopefully someone more knowledgeable than I can come up with a formula that works for emitters! At least I was able to back into it using the Water Use It Wisely site. (Yes, I know I can go out and read the meter and it will probably be more accurate, but my meter reads in cubic feet which means yet MORE calculations, albeit easy (1 cubic foot = 7.48052 gallons) - I was just hoping for a simple mathematical way to do it).