Are there several different positions where the quick release brackets and posts are installed depending on the accessory being used or is there one standard position for the posts?

 

You can turn the bushings around to get a different spread to fit the component that you're attaching. It's a minor change but one that you may have to make if the backrest or luggage rack (or whatever else) is too tight fitting or too loose.

Here's a screenshot from the instructions showing what I mean:

 

I believe the above post says it, but there are no real different positions... "Per sey" They need tweeking to fit any of the items. I bought a used tour pack from someone here in NC. Rode to Charlotte to meet him to pick it up. (he was a couple hours past it from me) When I went to put it on it wouldn't lock. We met at an HD dealer. They were kind enough to adjust mine to fit.

 

You can adjust docking points with washers to make different accessories fit. There are 2 pt and 4 pt docking kits and also depends on if you ride with a solo seat or 2 up.