Just wanted to share this drill. Been trying to do some left arm only pitches, but would get inconsistent contact (mostly fat and thin shots). Then started trying left arm pitches with my right index finger (simulating PP#3) also touching the grip. The reason, in TGM, PP#3 is what guides the force. In a left arm only swing, I couldn't control the clubhead. With only the index finger, you can't add right arm force. Hope this helps.