^the pure anatomy of the front shoulder when pressing from behind the head does not effectively contract these muscles.
Plus its a lot of strain on the supporting ligaments. Kinda like doing a wide grip pull over behind the head. The muscles are not aligned in that way to benifit from lifting at that angle.
Try Arnie Presses for shoulders, overhead throws with the med ball, twisting overhead throws with the med ball for some variation to your shoulder exercise.
Psalm 144(1): Blessed be the Lord my strength which teacheth my hands to war, and my fingers to fight.