We all agree the barrel gets delivered to the ball, but this doesn't explain what you mean by "you promote TTB" but not "forced supination".
Apologize if I'm missing something in your explanation here
Julray,
It could be viewed as an oar lock effect with the top hand. Meaning it turns naturally.
The hands have to be used early. It’s not something you wait and use them late. You don’t want to wait until bat lag and then use the hands. You want the the top hand to pivot and create an arc from the start.