Any reason not to place PVB ahead of ASV?

I need to replace a broken inline valve in my (3 zone) sprinkler system and my landscaper recommends going to above ground ASVs. Plumber says this is fine with local code. However, I'm concerned the anti-siphone of the valves alone may not be sufficient to protect the potable water supply in the house. Am I wrong?

Is there any reason not to do a main PVB before the above ground ASVs to 'double up' and ensure no backflow into the house water?