Here ya go, I found a pic online for ya.
Put a little Kamm on there like I'd make it, and it is at 10° overall, it is curved, so it is a bit shallower at the top.
The over all shape is below the curve, but I think this helps based on what I see several automakers doing. Most notably on the Honda Fit.
I think it is still not too steep so flow remains attached, but it closes the angle on the wake reducing its size.
If you make it flat, you'll want to be more like 7° because the 10° transition will cause a flow separation that won't be made up, and it will negate any real benefit of building a Kamm.....other than a sun shield for the hatch area
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The Kamm you have now appears too steep in my estimation.
Bigger Image of the same pic.