So given the rain we have had over the past week I have been able to see the difference in airflow over the hatch in the mist and water droplets. At ?55mph it looks like there is a lot less turbulence and its far more directed. Before it used to suck in from the sides to the centre of the glass with what looked like a fair amount of force but now it just goes strait down the hatch from the underside of the wing and with barely more force than water droplets rolling down the glass purely from gravity. I made these nifty arrows to illustrate:
Wingless
Winged
Aerodynamics are cool.