Don't let the fact that the lead heel raises up in the BS lead to a conclusion that there is little or no weight there. If you practice the move you will see that in order to perform a full backward rotation (pivot), the lead knee must move forward and in doing so the heel will rise. The weight is on the instep of the lead foot, not on the heel. It's said that is the reason for the extra spike on the inside of the shoe. He had one on the trail foot also which helped when he used the trail leg to push during the DS when using the right side later in the swing. He is said to have been quite flexabile and thus able to perform a good rotation of the upper torso during the BS.