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.
Look around your gym. Most trainees lack the calf thickness to suspend a pair of double striped knee socks, let along balance out the size and symmetry of the lower leg. Now look in the mirror. Are you one of them?