If our return line-loc was 4-5 inches under the surface, one might see a significant amount of siphoned water... Mine is just under, and my cornerflow drains lower than the tip of my return.
This is the reason for the siphon break - a small hole in the elbow either at or barely under the water line will break the siphon after a minimal drop in water level, so that if your loc-line return is a few inches underwater, it doesn't have to siphon all that water out before it ingests air and breaks the siphon.