AFCAD - slow to take off

Hi Everyone,I've noticed that traffic onto some runways start their take off runs fairly prompty while others take ages - creeping along the runway for a minute or so before taking off.I've just finished Olso Gardermoen (ENGM) and planes take off without fuss or delay from runway 1L.I downloaded EGLL off the library and observed planes taking off from Runway 9R. They joined the runway, and then crawled along the runway for 150 - 200m before stopping and beginning their takeoff run. It's really annoying, the number of takeoffs is greatly reduced whilst the queue keeps growing and growing.I've tried modifying the afcad, adjusting the angle of the taxiway to the runway, adding an extra runway node to the end of the runway etc. No effect! There must be some trick that can be deployed here.Any suggestions?