But notice that the vertical wiper is centered. Along the sides of the windshield the air is swirling around past the side pillars. If you happen to have a center wiper, that's a good place to park it.
Then again, the F1 has a single wiper that parks off to the side, and it's certainly designed for high-speed aerodynamics.
Edit: it's probably in line with the airflow going to the side and around the cabin. I'm sure the designers tested it.