Here's a topic that can go on for a very long time......
Completely dependant upon the area, birds, setup....
If I'm in a field, I set it up so I can swing across my body left to right with the possible entrance of the bird over my left shoulder and decoy out in front of my right shoulder. In the woods, I set up close on my decoy due to the fact that I cannot judge the new direction of the birds arrival.
If there's a creek around, I like to set up so that I can keep that decoy visible from the creek, if there's a valley, I get to the highest point, shoot from high ground.
Bottle necks are fantastic fun and may yield alot of failures before you get set up right...