I think it calculates from aircraft position to that FAF and then the rest of the flight plan regardless of your aircraft track or heading.you can check it out by setting intercept course to at FAF and you will see the same distance at progress page in different intercept track even your track is from the runway(outbound ).
Another method to check,by selecting the same track to intercept but change your intercept point (may be FAF IF or the others),the distance is changed (on aircraft or simulator ).
Last edited by Noknoipobin; 2nd Jul 2012 at 16:14.