So here is the Jeep Cherokee spoiler, not very much like a kammback:
And here is a kamm style roofline spoiler on the back of a Focus:
Whether either is what you want is hard to say.
What you do in fact want is a spoiler that brings your general shape closer to "the template," which looks like this:
Overlay that template on a good profile shot of your vehicle, probably by finding on online. Align the point of highest camber on the template with the point of highest camber on your vehicle photo. Then your roofline spoiler shape will emerge.