shrub sprinkler much higher than anti-siphon valve - problem?
We recently bought a new home and I have been inspecting the existing sprinkler system. The system currently has manual valves and I wanted to upgrade them to automatic. As I began reading up more about valves and sprinkler systems, I noticed that the system currently has anti-siphon valves installed. Now in all the instructions for anti-siphon valves that I've seen, it says the valves MUST be 6" above the highest sprinkler head. However, in both the front yard and the back yard (separate valves), there is at least one shrub sprinkler. The shrub sprinklers are 3-4 feet tall. The anti-siphon valve is no more than 6" above ground level, if that. Is this a botched job? Whenever I manually stop the sprinklers, I notice a rapid splash out of water from the outlet side of the valve. Am I right in assuming this is a backflow event being prevented by the valve? Should I remedy this situation? What are my options? I suppose I could raise the valve to above the shrub sprinkler, but it seems like it would be weird to have this 5 foot tall valve up in the air against the house wall. What do most people do in this situation? Should I just cut down the shrub sprinklers? Or perhaps there are other valves that do not have this height restriction? Does that anti-siphon backflow preventer still work or am I currently at risk of contaminating my water supply?
Thank you so much for any and all suggestions.
An irrigation newbie