Like most insurers, we cover conventional skiing/snowboarding only. There is no cover for any freestyle skiing, jumping, ski-flying or acrobatics, as the claims experience on these activities is very high.
You can ski in a Terrain Park, and use a rail, mailbox, tabletop, kink etc., (list goes on) without ever leaving the ground/feature. The rail (for beginners) for example, is a flat surface, which you can mount via the man-made snow ramp and dismount the other end using a same man-made snow ramp.
Not many people need freestyle ski cover anyway, but one specialist insurer who will cover you, for UK residents, is the Ski Club of Great Britain. Do note the premiums they charge do reflect the risk!