Extending the forend hand farther effectively changes the angle of the line of your shoulders in relation to the line of the gun.
That can create another problem in itself, when it comes to heavy recoiling guns, and/or high volume shooting. When the angle changes so that the axis of the gun is angled in an ever greater way to the body, the butt has more of a tendency to slide across the shoulder pocket upon recoil. If it's hard to picture, think of the ideal as having the axis of the gun at ninety degrees to an imaginary line drawn from one shoulder to the other. Recoil would be straight back into the shoulder pocket. The more that angle changes, the more the butt slides on recoil.
I have seen such severe evidence of that in Argentina that one fellow was bleeding through his shirt three days after returning home.
SRH
