A problem that people who hit the ball in the heel of the club is that during their swing, even though they may start with a real good posture, is that either on the backswing or the downswing they will move in closer to the ball. That could look like this on the backswing where they are actually going towards their toes, or they might make a real good backswing but in their downswing they are actually moving closer to the ball, which throws the heel of the club out into the ball. What you would like to have happen is that as you make your swing you want to maintain the same bend or the same posture throughout the swing. So at the top of the backswing you should have the same bend that you have at address, and certainly at impact, and then all the way in to the follow-through until very deep in the follow-through you should try to keep the same bend in your spine to allow you to make solid contact. I am going to enlist a good friend here to give you a drill that you can practice to get this sensation. What you want to do is set up next to a door jam or a wall at home and just cross your hands across your chest like this, one hand on each shoulder. Take your posture and lightly put your head against that door jam. Then practice making swings keeping touch with the door jam. You turn all the way back, all the way in to impact, and then all the way trough keeping the same posture throughout your turn. By engraining the sensation of using this door jam you will find it will be much easier to produce solid contact and not lean in to those shots which make you hit the ball off of the heel of your club.