On the test/practice bench, I'd have the 4F about a foot above eye-level, so I can stand comfortably, and still tip my head back far enough to use my F$#E%^G bifocals...
Figure out for yourself what's comfortable. You can practice it in your head, or pantomime the movements, to get a feel for what height will work best.
Don't forget, when you're doing it "for real" on a job, you don't often get a choice, but in the practice cell, I suggest doing it as comfortably as possible. The fewer variables you practice with, the fewer things you have to sort through if you have a problem.
Steve S
