Dave,
Without actually measuring the fluid in oz a good guideline for a visual check would be. With the Trike level and the cover off so you can see the clutch assembly. The fluid level should be just over/at the bottom of the clutch. See approxment level line drawn on the pic below.
(Note)
To much of an oil level over the clutch can also cause issues.
I really would suggest filling it from empty with 38oz of oil and taking note of where the oil level is on your Trike for future eye or visual oil level checks.
I hope this helps.
Ride Safe,
Bill G
As you say too much fluid will cause the clutch to drag and shifting is hard.ThumbUp
With my old tour glide I have the oil level at the bottom of the clutch plates, a might under where you show your line but then again mine is old school.