@LiquidFeet, as I’ve never been through the process (after all, I’m a very part-time instructor and only a Level 2 at that), someone else should answer —
@Kneale Brownson already did so.
@Skitechniek, here’s my interpretation of the graph, the video, and integrating both with my experience. Wide skis, much wider than what you define as wide (say over 90 cm) cause different biomechanics than narrow skis. They result in pushing the ski in the late shaping and finish phases of the turn and use different mixtures and intensities of muscles. Our exams have a skiing element where the examiner looks at the ski performance you obtain for requested maneuvers (these are selected to isolate and demonstrate ski performance). If you’ve never learned how to maximize ski performance, you are unlikely to pass Level 3. Pushing the skis is not what the examiners are looking for. So if you are skiing on a tool that biomechanically results in ski performance that’s not what the examiners are looking for, you’re not likely to pass. A narrow ski is better suited to learning the movement patterns that result in the ski performance examiners are looking for.
Showing up for an exam on skis that are wide could give the examiner a hint that you might not own the movement patterns they are looking for.
Mike