Jim, I had a look at my setup and there's no gap on mine. The end of the alt is hard up against the backing plate. There is a slight chamfer on the end of the alternator though. Aren't you just measuring this chamfer?
The position of your alternator depends on the cylinder covers, fan shroud, backing plate, alternator and pulley.
My engine has all stock genuine VW parts, from the cylinder covers through the fan shroud, backing plate, alternator, top pulley, and bottom pulley. If you want to check out any stock parts, I have extras of most of these parts.