I agree and have similar discussions on other boards. While the S197 could be classified as a fastback, it's more of a 2+2 than a fastback, thus the reason ford calls it a coupe. To me, a true fastback has an uninterrupted line from the roof to the tail panel. The S197 doesn't. It has a prominent interruption in the roof to trunk line.
Anywho, here's a quick attempt at shortening the rear end to make it more of a fastback. No hips or continuation of roofline, though...
I couldn't agree more, as your definition nailed it 100% right on the mark !