[WernherVonTrapp]

With my math, I certainly cannot provide the assistance that I think you need. Bearing that in mind, please bear with me as I try to understand why you are trying to figure this out, which if your math answers are correct, you already have.
The Fire Control Manual that you reference seems to have been distributed in the 1950s, after WWII. Is it possible that some postwar modifications had been made? Additionally, according to the official USS Cobia website (the sub from which that Fire Control Manual belongs), that particular Gato Class sub was a product of the Electric Boat Company of Groton, as opposed to the Manitowoc shipbuilders which also built Gato Class subs.
Might some of these variables account for the discrepancies that you point out? Again, my math is about as sharp as a soup spoon so I cannot offer assistance in that manner but, I am trying to aid you in an alternative manner.