Dieter Dworkin Muller writes some good stuff about heater 
     observations...
     
     Glancing through the my 1964 owners handbook, the section on heating 
     says that by opening a cab side window or a vent wing the amount of 
     hot air flow will be increased. So your observations are exactley how 
     the system is designed to work - according to VW anyway.
     
     Lee.