What counts as a tributary valley in Davos?

Im looking to travel to Davos in February and will likely be making considerable use of the local public transport network. This page with information about lift passes (which I will have) says "regional ski passes, issued by Davos Klosters Mountains, are full-time valid on local buses during the winter season as follows: VBD = Local bus network Davos without tributary valleys" However, I have been unable to find out exactly what counts as a "tributary valley", does anyone know how far out these regional lift passes are valid on the bus network, and specifically, if they can be used to return from the two itineraries from Jakobshorn (Muhil & Teufi).