My opinion is from 1-25 yards you should be dead on if your sights are aligned and your shooting form is proper. If anything, a difference of a 1/4 inch should be the max at the distances mentioned, if at all. Bullet weight and velocity may be a factor but small, not 8 inches low shooting from 15' to 10 yards(sounds like form problems and flinching to me). If I were you I'd benchrest the pistol at 15' and in single action slowly squeeze off some good shots to determine if windage is an issue, only then would I drift the sights. If your dead center on target at 15' you will be dead on at least out to 25 yards and perhaps 1 inch low give or take at 50 yards depending on the velocity and weight of the ammunition used. In other words a pistol at combat ranges is not like zeroing in a 30/06 at 400 yards.