I wondered if yours was starting (at rest) higher than it should be, because that would explain why it's sweeping too far.
On previous car's I've had the wiper arm was just pushed onto a splined attachment from the wiper motor, so you could pull it off, rotate it slightly, and then push it on into a new (higher/lower) position.
I wonder if yours would be better if you repositioned it so that it sits lower ?