Driving around with the rear windows open?

[imzjustplayin]

I remember reading somewhere that if one could, driving with the hatch window open can improve fuel economy because it reduces the amount of negative pressure that is being created behind the car. Well today while I was driving around, it was really hot, between 95F and 105F, in a black car with black interior not using A/C and so I opened the front windows as much as I could during speeds of less than 25mph and kept them closed above that.

Well I thought about the pressure thing with the rear hatch windows and so I opened the rear passenger windows about 1 inch on the driver and passenger side, looked at the computer and noticed the fuel economy improved! I couldn't believe my eyes so I closed the windows again and saw it drop, opened them again and saw it go up again. I tried this several times and while I generally saw a consistent improvement in instantaneous fuel economy, the road elevation tended to vary greatly and so it made it really hard to believe what I was seeing.

So as I was driving, doing my errands, I tried the best I could to find a patches of area where I saw the computer was holding its reading, where the elevation stayed the same and the surface was the consistent as well, then I would try my A-B-A testing with the opening and closing of the rear windows for a long enough duration to get a steady reading from the computer. As for why I didn't open the windows more, it's because when I opened them more than an inch, I saw the fuel economy drop and I figure that's because it would create too much drag since I can't open/remove the back window at all, so the incoming air would just smack against that instead of escaping.

Has anybody verified doing this, I mean just opening the rear windows slightly w/o being able to open/remove the back window (above the trunk) at all?