The more players that I work with, the better feel I get for what are relatively easy corrections to make and what are more difficult. I’m learning that one of the hardest habits to break is the ball going back behind the player’s head.
When I worked with Louis Amundson (then of the Phoenix Suns, now a Golden State Warrior) we developed a catchphrase of HAIRLINE. That was my one word reminder to him to get his index finger close to his forehead. Almost having the nail of his index finger graze his hairline. It is now an expression that I use a lot with players trying to break the habit of bringing the ball back over their head. Because this happens quickly during the course of their shots it is difficult for players to feel the issue so take it slow.
Focus on touching your index finger to your hairline and break that tough habit.