Yeah it was actually the dry run prototype that was kicking around from the project with the Nuvinci unicycle, where I needed the shape done this way for stiffness along the chainline to the jackshaft which was located behind the seat tube:
Without linking the pair of curved tubes together though it has quite a lot of flex in it, so it’s not an ideal design as built but I like the curves and elegance and it seemed a fitting frame choice to use with this build.