Try a different approach, like starting you shooter low, and using him as the screener for your talented post player by back screening. What this does is to force the shooters defender to temporarily help on the post who's a threat nearer the basket which give the shooter a quick step out for the shot. You do have a problem though if teams get in the shooters face and force him to put the ball on the floor. My experience has been most shooters can put the ball on the floor but lack the confidence to finish strong to the basket. This fact alone discourages them from feeling comfortable penetrating.
Most penetration fails because the offensive player takes too small a penetration step.
This occurs as a result of floor foot and ankle flexibility. The defender-side hip must power through the defender, and the penetrator must sprint to the ball after it's been released. Breakdowns occur because the penetrator is too high, off balance, or doesn't have the wrist on the penetration dribble hand in a 90 degree cocked position to provide the most effective push. If the penetrator releases the ball after pushing off the back leg it will be a traveling violation so make sure you don't let them practice this technique improperly. Additionally the initial dribble often doesn't clear the defenders foot position which places the ball to the side or even behind the penetrator instead of in front as they attempt to sprint past the defender.