As projectiles count things that are small enough that they can be blocked by a shield if they are not of the kind that ignore shields. I think they need to have a flysprite and no AOE. So the darts from iron blizzard will be halved in number but the AOE fire breath from the fire drake, not so much. I think. I have not tested this. I should always make that disclaimer.
Hmm, so you think it works on projectiles in particular? That makes sense mechanically, though it's disappointing in a game sufficiently detailed that gay men can't be seduced by women for ethereal bolts that have no problem ploughing through water to be stopped by high winds.