3dplane -
I did (what I hope is) a closer analysis. When I shift the center-of-camber forward, I get a 7.7 degree slope from the edge of the roof to the vertical line denoted by "30" :
When I look at the profile of the Protege, I *think* I see a roof that is taller in the back than other cars, most probably for the sake of rear seat headroom. Therefore I think that your stated slope of 12 degrees is too steep.
My Protege image is from tirerack.com, so it is decent but also subject to error. I had to rotate it 1 degree clockwise to make the tires line up.
CarloSW2