Rick,
It's not the angle that's the problem, it's the position of the thrust washer so when you adjust the cowl to center on it the cowl may be pointing up or down which makes it not square to the backplate. By turning over the mount and placing the engine on top of it (inverted of course) it places the thrust washer in the center so the cowl is in the proper position.

I wish I had it here to take a picture because I don't think I'm explaining it well enough.