Thanks, Ted. Your analysis is exactly what my online research revealed, that full weight transfer to the front leg will effect back foot lift.
As for his hitting, he's hitting very well. He spent the past two-and-a-half months of summer (May 15 - July 31) on a 13/14 "training team" run by a local high school coach and former MLB pitcher that focused on core strength conditioning, speed training, batting, and an occasional field practice. No games. He's taken thousands of swings in the batting cages this summer; maybe that, along with the core strength conditioning, led him to develop a full weight transfer that he didn't have before?