Tapping oil galley plugs issue??

[95gt444]

I tapped the 3 plugs in the front of the block with a 1/4x18 npt tap just like everyone says to do. The tap seems to small as the threads dont start till about 3/8" in flush from the block. My main concern is the one plug will actually block oil from the front main journal cause the plug will block the oil passage?? Any ideas??