Serpentine belt alignment
 

The pulley located on the spring tensioner appears to be about 1/4 inch wider than the width of the serpentine belt.

I make an assumption that when the BMW dealership changed the belt a few years ago, they aligned the serpentine belt on the tensioner pulley exactly in the middle of the pulley. If they did, there would be a small empty space on the pulley today towards the radiator and also a small space on the pulley towards the firewall.

Two questions:

When most of you are putting on a new serpentine belt do you align the belt exactly in the middle of the pulley or doesn't it matter?

If I loosen the tensioner and move the belt exactly in the middle of the pulley, would I find the belt comes back to the front edge of the pulley closest to the radiator again?

If the pulley is on the flat side of the belt, it will ride naturally to one side or the other depending on any minor misalignment/tolerance of the tensioner. Moving the belt will only have it go right back. If the belt is fully riding on the pulley, you're fine.

@scottalexander, I believe the belt should be align to whatever position the rest of the pulleys favor. Like @audiophool said, as long as the belt is fully riding on the pulley, the system would do its job, and you should be fine.