The problem with moving it forward is it DOES screw up the geometry involved in the sight line and trajectory convergence.
For argument's sake let's consider the boreline instead of the trajectory and sightline. They make up two legs of a right triangle, with the third leg being the distance from the bore line to the aperture of the rear sight. If the bore line is level, then the sight line must angle downward to converge at the point of impact. (Yes, I know, we're ignoring ballistics, but the principle is the same.) The line from the bore to the aperture is vertical.
Draw you a right triangle representing this example. Make the base say, 12 inches long and the vertical 4 inches high. The top of the vertical will represent your sight aperture, and the point where the "sightline" and "boreline" meet is your Point of Impact. Halfway along the horizontal line draw another vertical line connecting to the sight line. This will represent your front sight.
Now move toward the convergence of the sightline and bore line about two inches and draw another vertical line 4 inches high. This is now your new rear sight position.
The top of the new vertical line is now above the sightline.
From this diagram, it is easy to see that if you move the rear sight forward, you are going to have to lower it to keep the same point of impact.
I quit. My head hurts now, and I last took geometry in the Johnson Administration.
Lonny