The rendering you reposted and the experiments I did with redwood strips suggest that the transition from the greenhouse cross-section to a nice Templatey half-circle can begin at maximum camber(generally at C-pillar) and angle or curve back to about the middle of the quarter window.
I'm working on a more permanent (i.e., roadable) boattail, it will be about half that height so it doesn't affect engine cooling and not have the reverse camber.
The breakthrough was realizing I can hand bend the parts over an old water heater.