Quote:
Originally Posted by eagle
can you elaborate on that with a crude drawing on top of my photo?
also, took a picture after few days on a dusty road, notice that the sections in the sides have less dust than the center section which does not have a hole....so this means....what ? that the holes are working or not? 
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I don't know how to draw online. Sorry! What you're looking for would be like the 1987 Renault Vesta-II or Mercedes-Benz Bionic car. These are both 'Kamm-back' cars. Chopped off at the back like a loaf of bread.
For the limited length we're talking about,you can't expect to see any significant gains,although you'd be set up for boat-tailing should you ever choose that.
The slots on your 'wing' provide a downwash to help prevent dust from the turbulent wake from accumulating on the glass.
If you had a horizontal rubber fin,on the edge of the hatch,just above the blue oval badge, this might help keep some of that dust sequestered away,but it would need to be rubber,for pedestrian safety.
With that,you could extend your 'wing',seal those holes, and enclose the sides;creating an air-tight cavity,which would allow a little flow deceleration and higher pressure before separation,leading to less pressure drag.
Any meaningful drag reduction could only come from a box-cavity or boat-tail. Hucho has personally tested both technologies and they're the only two devices that ever 'showed' drag reduction.(the 2016 Mercedes-Benz IAA concept does this with an extensible boat-tail section,a lineal descendent of Fachsenfeld's FKFS design of 1935 for the K-cars).