I only put the ball behind center to control trajectory and spin. Use a small range with wedges to control these. In my experience, moving the ball back makes fat shots less likely (thin shots equally more likely though), so there may be something else going on (swaying or extra movement). There is a phase where playing an iron from middle stance is good, but long term I've moved my back foot forward slightly until pw was slightly in front of center, depending on the club. Some people play all irons from middle stance, so it is best to find a position you are comfortable with, without manipulating your swing.
