So the anti siphon valve you have is meant to directly feed water into a sprinkler zone — not as a backflow valve for an entire system. See https://www.irrigationtutorials.com/irrigation-backflow-preventers/#asv
“1. Never install an anti-siphon valve upstream of any other valve. If you do the anti-siphon valve will not prevent backflow and you have wasted your money buying it. (Exception: drain valves are OK installed after an anti-siphon valve.)
2. Never use an anti-siphon valve as a backflow preventer installed on the mainline upstream of other valves. This is a common error that a lot of people make. I have heard employees at home improvement stores recommend installing an anti-siphon valve as a backflow preventer with standard electric globe valves installed after it for each of the sprinkler zones. I have seen many contractors do this also. Both should know better! Don’t you do it!!! It will damage the anti-siphon valve. Plus the anti-siphon valve will not prevent backflow when installed this way. You are no better off than if you didn’t use a backflow preventer at all. (Contractors and suppliers: before you flame me for being wrong, do some research. Don’t embarrass yourself! Most anti-siphon valves have a warning on the box or in the installation instructions about this. Just read the instructions!)”
Others will chime in but I’d recommend using a different type of back flow preventer — the irrigation tutorial webpage has a decision tree on deciding what type to install.