Have you ever wondered why your trigger shoe moves to the front or the back?
The reason is that your trigger finger must rest on the trigger shoe face exactly at 90 deg. This way, you can pull your trigger backward in a straight line, as shown in the video.
However, if the trigger shoe is too much in front as shown in this video then your trigger finger makes an angle on the trigger shoe, and it pushes the trigger to the left as shown in the video, and your group is also formed to the left as shown in the video.
On the other hand, if the trigger shoe is too much at the back, then your trigger finger curls around and pulls the trigger shoe to the right resulting in the groups forming on the right as shown in this video.
And that is why you should place your trigger shoe in such a way that your trigger finger lies flat on the trigger shoe face at exactly 90 deg. So that when you squeeze the trigger, you pull the trigger back in a straight line and your groups form in the center as shown in the video.
Have a good day. Happy shooting.