You want the ball in line with your right foot. Ball too far in front and you hit the ground first, then catch the ball with the back of the stick.
Ball too far behind and you hit the top of the ball, or pull it way left.In games the ball is moving, so the real skill is this: Move the ball on the correct line before you strike.
Pick your target in the goal. Imagine the line from the ball to that target. Your stick angle needs to be perpendicular (90°) to that line.
So when you set up, your touch should move the ball along the same line your stick needs to be on. If you get the line right, the backhand becomes automatic.