Jim,
A 300 gr 45 bullet using nominal inputs would have a drop of ~9.9" in 100 yards. Your sight difference is .16" and that equates to 9.6" at 100 yards. (using the 20" SR)
I guess the confusion is, which is higher over the line of the bore, the rear or the front sight. If the rear then every thing looks correct; however if the front is higher then the bullet would impact about 20" low.