Ron,
You process is fine. .. .you're doing exactly what you should be to GB. It might be helpful to 'intentionally' go the other way. . . .turn it to far, and get the signal to silence when you get close to the ground. Unlike the older 10 turn pots, the newer 3-3/4 turn pots get there quick, so you shouldn't have to turn it much. At that point, gb is some minute' setting between the 2.
As to the signal change when around an inch from the ground: go slowly toward the ground during GB. Not so slow auto tune keeps it consistent, but not jerky or quick movements either. Experiment with the different speeds approaching the ground and lifting it back up. Once you figure out the speed and get used to the adjustment range of the GB control, you should be able to get it to maintain a consistant audible at an inch off the ground.
Keep in mind, some MD's are more 'sensitive' then others, and can react to very minor changes in mineralization and conditions (wet, dry, shade, sun), and going from one to another might require tweaking the settings. You'll be blind to these changes slowly occuring when running in discriminate only, so, periodically switch over to All Metal. . ...or hit the trigger... .and check to see if your settings are still intact. I do it constantly with the Vaq by holding the pinpoint button and doing a quick check. It makes a difference.. ..I've had to adjust 1/4 turn on GB between the front and backyards of a single homesite.. . .that's a big difference for such a small area, and not necessarily all that rare.
Be patient, you'll get it, and it will become second nature to you. HH
-Ric