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Originally Posted by ebacherville
how about this..?? its extreme but what the hell.. 
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ebacherville,read your post and will touch on your points mentioned (all good!) (1) The flat portion on my CRX moves the the back of the car to the point where it intersects the ideal roof curvature.And yes,there is a captured-vortex over that portion,contained within the C-Pillar extensions.And as in a "bird-bath" rear spoiler,air above, scoots over the vortex as if its a solid body.Yes,there is a small penalty to drag,however it allows uninterrupted rear-view vision.Should you attempt to angle the glass up to the ideal roof slope,light refraction would destroy your vision,as all you would see is internal reflections of your car.(2) By running the slope at a steeper angle to achieve a smaller rear section,you shoot yourself in the foot,as the flow will separate,and your new tail will be in a region of separated flow,with no lower drag than before.Please look at my installment on "roofline" I posted a few days back.(3) The bottom of your boat-tail begins above the line defined by the bottom of the car.I'm putting an installment together for "underbodies",however I'll go ahead and mention if I haven't,that the flow under your can not follow an upsweep of more than 2-1/2 degrees.With what you've illustrated(and I'm not trying to beat up on you),your under car flow will never touch the under side of your boat-tail,and will just be surrounded in turbulence.(3) The aft body of the airplane that basjoos posted,you must remember,is in free air,high above ground-effect.For that tail to work with as low as drag close to the ground,it would have to be stretched to twice it's length,and all those curves would have to be twice as gentle,to prevent separation do to the "mirroring" effect of the road surface.(4) basjoos' CIVIC is a 3-door hatchback and has distinctly different aerodynamics than our CRX's.His roofline is further from the road,is less effected by ground-effect,and because the sides are also converging as the roof is dropping,he gets away with no longitudinal attached vortices,which can be the highest drag component for a "fast-back" car like the CRX.Take a look at the 1978 Mercedes-Benz C-111 record car.You can GOOGLE it,and there's even a plan view of the car showing the boattail detail from above.I'm excited about your project and want to steer you around any obvious snafu's if I can.Ive tried to force the atmosphere's hand before, only to have it laugh at me good and loud.You can't cheat the sky.