Your headed in the right direction,and as soon as we get an image we 'll be able to tell about the downslope.
One thing I want to mention is that these rooflines need some softened edges where the roof and sides come together.With a hard intersection they're prone to create longitudinal vortices which have remarkably high drag.
Here's an image of Kamm's personal car and one of his wind tunnel models with the hard edges.You can see the tufts 'flying' into the vortices,the whole length of the car.
