Re: AI 45MOA scope mount
If I read the specs of that scope correctly, it has 26mr of total elevation travel, which I would expect to be 13mr up and 13mr down from the optical center position of the erector. The 45MOA canted rail would give you all 26mr in the up direction, but you lose about 1.5mr for a 100 yard zero. So, you should have about 1.5mr down and not 8mr.
You can check the total elevation travel of your particular scope - there will be differences from spec simply because erector cell parts can vary slightly in size, which could affect total elevation travel. You might also have unequal up/down elevation travel, but still have 26mr total travel.
Bottom line: I think you're correct, it's too much downward travel with a 100-yard zero.
PS I hope you understand how to set the turret zero. To confirm that you need 8mr for a 100-zero, you should confirm that the erector is actually moving that far below the 100-yard zero point, and hasn't stopped moving much earlier.