[Bagger Lance]

Spike,

Instead of focusing on the left thumb, try shifting your focus to the last three fingers of the left hand; the #2 pressure point.

Feel those last two or three fingers load at the top of your swing or alternatively during your start down.

Sustain the lag on pressure point 2 with your pivot motion until you get an automatic release. If you nurse this feel enough, you will feel a dramatic loading and unloading sensation and your awareness of your left thumb will slowly fade into the background.

If you want to manually uncock early, then use those last three fingers to accuate the uncocking motion. Pressure point 2 unloading is very sensitive to an early throw. It doesn't take much action to make it happen. In my opinion, its much harder to sustain PP2 lag load into an automatic release.

The role of the left thumb is primarily structural support. It should be inline with the #3 pressure point.