+P shock wave?
I won't disagree..... the more pain I can put into the BG's the better. The question ends up being; in many shots more than 13" = outside the torso. So is the energy wasted?
I've thought about this a bit from a physics perspective...
I think of the hydrostatic shock as a "wave" in human flesh created by a projectile. For the attacker to feel that wave, it needs to be as tall (amplitude) as possible.
Next, think about making a wave with your hand in a bathtub. The strongest wave is created by pushing the water constantly. If your hand slows down too much as it moves through the water, the wave won't be made, because waves are created by matter that's displaced at a constant speed... The force creating a wave should go at as constant a speed as possible.
Thinking about a slow bullet passing through flesh, especially a hollow point, a dramatic slowdown occurs. If the bullet stops before it exits the body, then it was slowing down for a long time in its path through the body. Its speed was not anywhere near constant. I wouldn't expect much of a wave to be created by such a projectile.
For a quite fast bullet, let's say the .357 Magnum, the bullet tears through the body hardly slowing down at all. I've heard the phrase "struck by lightning" attributed to the effect of this bullet. Since the bullet was very fast, and hardly slowed down, it was traveling at a more constant velocity during its traversal of the body. So, it makes sense that a very strong shock wave was created. Hopefully, as the wave traveled through the body, it affected many parts of the nervous system and overloaded the brain with input.
This particular effect may be lost on assailants who are on drugs that disrupt their nervous system. But of course, the bullet will still do a number on whatever it went through.
Anyway, if this hypothesis is true, then overpenetration goes hand in hand with an effective "hydrostatic shock" effect. Be sure of your target and what is behind your target...
Physics majors feel free to debunk my layman's understanding of wave dynamics.