Distance from the wall will give you less reflections from the bass ports.

The angle helps identify the sweet spot and get the best possible listening position.

I would recommend you just take this as is, because this is science stuff that has been tested to give every studio around the world a more "cohesive" perspective on how to mix and listen to the music.

Basically it's a way to give you the best sound and make sure you can translate what you know else where around the world, in any studio.