[robertifly]

Bean, on the depth of the siphon, are you speaking of when running or when DT is drained fully down to sump?
When running the siphon is 1" under water, when DT drained down siphon 4.5" under.
When running the open channel under 1-2". open channel 4.5-5" under.
The only other measurable difference in the two is the valve in the siphon drain, the air line in the open channel and the open channel measures 1/16" higher at the bulkhead.
All those factors should give the siphon drain the edge, yes?
I have not drilled the hole at the water line yet, I'm thinking that would be at the water line with DT drained down?