He is a lesson in gripping the pistol that I give shooters to help with their accuracy and precision.
Hopefully this will help you, I used to shoot 25-35K rounds a year and it was the one thing that I always kept in the forefront on my training sessions.

Hold your finger at 90 degrees with your wrist straight and elbow down out if front of your body.

You will see that when you do pull your trigger the result is a angled pull which results in a lower left hit. If you are doing the same trigger pull on a a rifle it is effected less due to the extra weight.

Now try the same with a slight bend in your wrist.

The bend in your wrist is necessary to give you the "more" correct angle to have the trigger come back clean. As you grab your gun, do everything the same but angle your wrist out about 10-20 degrees, it makes a huge difference in the angle of your trigger finger.

For me I only have the pad of my finger on the trigger, I see others all the way through due to hand size. The important aspect is to have your finger coming back at the correct angle.

The most important part of the trigger is maintaining the correct angle of the wrist/finger. As you shooters adjust their grip when learning something new they tend to go backwards. To see if your wrist/finger is in the right position, look a small gap in between your finger and the gun. Whether I am shooting long range or pistol I try to maintain this gap. It also allows you feel the trigger break better without resistance.
Jerry Miculek would build his grips up at this area to maintain that position since the revolvers had a heavier pull. Try it and see if it helps your groups.