How you hit the shot will depend on what kind of ball you are getting, where you are at in relation to the table, and what kind of BH topspin you want to make!
Your stance (wide is better) affect this, as well as how well you can accelerate the bat to max out at impact. The different parts of body work together to increase speed and power (and spin) Leg bend, trunk twist, shoulder twist setting the shoulder and elbow point with upper arm, using the lower arm to continue acceleration and the wrist to finish it all off. All these parts work together to strike the ball in the optimal strike zone to maximize efficiency.
The reasons a lot of players fail to make spin, speed and control are...
-poor position #1 reason for most BH shot must be done in a very good position or it will be a fail under pressure
-poor balance
- not wide enough or too upright
- failing to use the lower body
- extending the elbow too far out
- using the shoulder joint as a main pivot and using the arm locked as a whole
- hitting the ball out of impact zone (usually hitting way too far in front) sometimes it is a position issue, sometimes it is a player vision or form issue
- failing to use enough wrist