[Tom Goldman]

I would not say there is an optimum height , but more a minimum .
I went from a low profile conventional scoop that was 3 1/2" above the air horn to a triangle shape that was 8" above the air horn.
There was a substantial improvement in performance ,2 MPH and more even O2 sensor readings across the cylinders.
I also feel having a radius on the entry to the carb is very important ,I try to use a 2" radius bell under the tray on all the scoops I mount.