A desirable ball position puts the ball at a point that allows the bottom of the swing arc to meet the ball first on contact. The bottom of the swing arc is normally 2 to 3 inches off the inside your left heel. The distance you  stand from the ball should change and is predetermined by the length of the club. Usually the butt-end of the handle should rest approximately one fist away from the inside of your left thigh on all irons and two fists away for ther driver.

As the club gets longer so you stand further away from the ball.  Your right foot moves slightly further from your left foot progressively on each longer club. Typically for a pitching wedge the outside of your heels are matched up with the inside of your shoulders and for a driver the inside of your heels are matched up with outside of your shoulders. This puts your spine progressively further behind the ball on longer clubs and more over the ball on shorter irons. This allows for a proper angle of attack at impact for each club. A steeper blow is needed for shorter irons, thus the spine is kept over the ball and a sweeping blow in needed for long irons thus the spine is set behind the ball. The left foot always stays in the same position relative to the ball, the right foot only moves to widen the stance on the longer irons and set the spine further behind the ball. So, basically this is considered only one ball position. Keeping the same ball position in relation to the left foot makes ball position easier to understand and easier to reproduce. One of the exceptions to this rule is the driver. Place the golf ball directly off the inside of your left foot on the driver because it is teed up. This encourages an ascending blow instead of a descending blow which is needed because the ball is elevated above the surface of the ground using a tee.