to clarify one thing, that six inches is above the highest head on that valves station. that being said there is no reason you can't raise the valves that high besides needing a ladder to work on them.

thanks! one more question. can i tee off the main water supply line - run pipe to faucets for drip irrigation (which would have back flow preventer and filter etc) UPSTREAM of the anti-siphon valves? meaning.... one pipe would feed three lines for drip first, then a shut off valve, then antiphon valves. like this: (pic is sideways)

yes you can. your layout looks good.

excellent! that's what 150,000 hours of research can yield for someone who has no idea what she's doing. thank you!

Did you end up installing your anti siphon valves 7ft off the ground?