Does the leather pocket pinch of slingshot not parallel to the rubber band affect the trajectory?

Standard posture can help you stabilize your posture as soon as possible and reduce the impact on your trajectory.

The key to the position of backhand and the angle of head tilt is to find the most comfortable posture that can accurately hit the ball. This posture is not uniform. As long as you hit it correctly, you will still use this position next time. Practice a few more postures, and you will be basically stable.

As long as the posture is fixed and stable, even if you have a posture that is not standard, you can adjust the forehand aiming point to make up for it.

So the slingshot posture is not uniform, or those two words, steady. Not today, not tomorrow. As long as you play correctly, practice every day to find this posture that can be played correctly. Then constantly consolidate this posture.