I have two 12" siphons in my pond. The normal flow only spills through one of them, and a good rain will flow through both. I don't believe they have ever gone into true siphon mode. I am very happy with the way they work so far. I am looking forward to seeing what a 12" siphon can do, though. I bet it's a sight to see.

Hey Moe, I'm trying to think but nuthin's happening!