Rather than trying to touch the bar to your chest or reaching your chin over the bar (both of which can produce dysfunctional mechanics), the goal should be to achieve proper upper back and lat activation. This requires several components.
Dan John is Testosterone's Yoda, wise as hell but with better skin and a heckuva' lot higher PR in the snatch than the original. However, our Yoda has had his share of Yodas to learn from. Read here as he shares his most valuable weight-lifting lessons.