On a fixed pitch prop the physics would point to wide open throttle for least drag.
But the mixture must be full back, no avgas being pumped into the a hot exhaust and ignition off. I think instructors teach closed throttle just in case the engine has a sudden spurt which could affect your aiming point or tempt you to climb out then fail again. Once you are committed you are committed.
The other interesting thought is an air start from a stopped prop. Fully open or closed ?
Open may take more power to get over the first compression stroke but spin faster once spinning. full closed may take less power but spin slower so they may be nothing in it. The best position could be half throttle a balance between the 2 settings would need an air test to find out.
Last edited by horizon flyer; 5th Jun 2017 at 15:02.