Why do you want to fool with the front sight height at all? You can do this elevation zero job using only the rear sight - remembering that the markings are meaningless with non-standard ammunition.

If I understand your description, you are hitting 4.5" low at 50 yards (let's assume that's below point of aim since you don't specify your aiming point or hold). All you have to do is raise the rear aperture enough to put the POI 1/4" above POA at 50 yards. (That should be some 9 or 10 clicks from wherever it was when you shot the 4.5" low group). POI should then be on POA at 100 yards and 5" low at 200. Add 2 to 3 clicks to bring POI to POA at 200 yards. These calculations are based on Prvi's published MV of 820m/s for this load, front sight .8" above bore axis, and a BC of .375.

Here's a little graph of the trajectory with 100-yard zero. Click on it and it should become big enough to read.

Attachment 54093

If you use a 6:00 or other below-center hold, add enough elevation to compensate for the difference between POA and target center.