This confuses my brain: "Which means 10MOA under plus about 3.75 MOA that the bullet dropped at 425yrds puts me at about 13.75 moa when my scope is zeroed. That is about a 1000yrd zero." Is the only way to remedy this to order a 20 min base instead of my 40 min base?
I can't visualize whether the 3.75 is included in the 10 MOA or added to it as you indicate. I have a tough time getting my head around those kinds of things.
The 20 MOA base isn't the only way to correct this though it would be the better way.
You could do the ol' pop can shim under the front.
Kirby would up-chuck his breakfast when he heard about it though.