Cheb was where west German flights were routed, like the first Lufthansa flights to Leipzig in 1989 or Interflug A310 delivery flights from Toulouse. The RAF would have been free to cross the inner German border but only to support the Berlin garrison. Going to the CSSR would have required some special permit south of the Berlin control zone to the CSSR border.
East German nav charts from the old days:
https://konbriefing.com/mad/approach...airfields.html