Keep your trail side back to shallow the club
The coach works on keeping the trail knee, hip, and side from getting in front of the arms and hands. He says letting the trail side move up in front pushes the arms out, and that keeping that space with the upper body covering is what shallows the club and gets it on plane; he adds that moving the trail side toward the ball will not produce consistent ball striking.
Channel: PorzakGolf
Watch official source at 5:41