Got a 12 bolt rear with a T/A cover. The fill hole is way above the axle tubes with this T/A cover so how much will this 12 bolt diff hold with this type of cover? I would wait till the fluild comes out of the hole in the cover but with it way above the axle tubes I would think this would not be the case since the tubes would have to completely fill with oil to be able to reach that area. I have put in three quarts so far.

I have the Moser cover (made by T\A). I just filled mine up to the bottom of the stock fill hole. If I remember correctly I think it took 2 qt's +the posi additive.

Use the factory fill hole, not the cover hole.
Poeple have complained about the fluid coming out of the vent tube because they over-filled the rear end using one of those covers. Just remove the factory fill plug and let it drain until it stops.... install the plug and you're good to go.