The more I look at the AMG style splitters, the more I realize that they were specifically designed for the lines of the C-class.

The crossfire has a few sweeping lines in the front, and the most obvious is the one which follows the front grill.In order to make the front splitters look like they were made specifically for a crossfire, one of the sweeping lines on the front of the car should be emulated in the splitters.

Now this is just an opinion, and I don't really know a bee's nest from a box of rocks and what you've already done with the foam prototype is more than I could do, but check out this picture I made, and see how the inner front lip's lines kind of mimic the line surrounding the front grill. It kind of flows with the lines of the car.