The dimensions are suitable for many vehicle models, since there is no fixed seat form. The terms you put virtually on the seat and the backrest can (lower portion where the seat is) an elastic band to use as a slip to prevent. Even the cover is slightly larger than our car seat, so you can see the protruding surfaces simply "bend it" and so protect the seat side. This makes it also suitable for many seat sizes.
Further improvements I could imagine another elasticated upper headrest area, so you can also protect this part against slipping.