Hi Slicepong, The index finger certainly does help control the bat angle for sure. That’s right it’s always partially closed on every forehand to avoid hitting flat and getting a good contact on the ball. As you said against backspin the bat angle is still closed but needs a slightly more vertical brush upwards compared to a slightly more close angle and more forward brush over the top of the ball when playing against topspin or no spin shots.
Seems like to me you’ve got the feeling exactly right in your head, glad you found the forehand hack video helpful, with more space from the table you will find it easier to build in more body rotation and weight transfer with time to stop it being mostly the arm as you said. Keep up the good work and let us know how you are getting on!
