IMHO that's a little academic. If you do happen to be attacked by a predator there's probably going to be very little time and checking the wind direction wouldn't be that high on my to-do list.

But I think it's largely a moot point. Even in a small pepper spray can the pressure is so high the stream can easily reach about 12 to 15ft. Bear spray has even better range. Unless there happens to be a tornado coming in your direction whatever attacker you spray within reasonable range is going to get a whole lot more of the nasty stuff in their face than you.

From what training I've done the person using pepper spray is likely to inhale a very little bit no matter what but it's not going to seriously affect you. Also remember, once you start spraying walk back slowly. it will help create some more distance between you and the threat, giving you more opportunity to hit him with everything you've got and it also reduces the chance of getting any of the spray in your face.