RE: Cathe and Ed. Crowd --- S&Heavy shoulder form quest...
Try to do both movements without weights with only one arm while holding your shoulder with your other hand. You'll feel your shoulder (deltoid muscle?) kicking in a lot more "with the twist" than with just the horizontal movement. But this is just my guess.
Also, try to do the Arnold press, I guess that's the same idea. It just moves more muscle than the traditional military press.