The top outside edge of the coaming should be well rounded. And so should the bottom outside edge. In fact a cross section showing these two edges whould show just one smooth radius. If you have sharp edges they may catch on the skirt, making it difficult to release.

I've used a neophrene Perception spray skirt on my two CLC boats. (Cape Charles 17 and Patuxent 17.5) It's a good watertight fit on the CLC cockpit. And I've never had a problem gettin the sprayskirt to release. I'm guessing that your boat's cockpit is about the same size as mine.