Maybe angle is the wrong word. Open or closed blade make more sense?
How do you know a shot is going glove side? Youre hopefully not guessing. Whether you are aware of it or not, goalies do process the blade. The difference in position of the puck at the release point is very small. Your brain takes in all the info including the position of the stick to determine it's going high, low glove or wherever.
I relate it to a batter in baseball. He's not just seeing the ball. He's sees angle of the arm, release point.
Obviously you can only do this on clear view shots.
Anyway that's what I used to do. Maybe I'm just an old fart now that did it different many moons ago.
Side note..I hope you're training these goalies to not go down on every shot. Going back to that slap shot goal. If Stolarz has his angle right and just stands there, it most likely hits him in the pads. I find goalies move way too much.