The fact that a centre fix is not a consistent point in space is relatively academic as the use of "route direct cfix rwy24r" is only used during the quieter periods. When you consider that one cfix maybe at 8 miles and another operators could be at 12miles on the extended centreline what difference does it make? It is no worse than sending an aircraft to a beacon outside your area of responsibilty, I defy any ATCO at manchester to know "exactly" where an aircraft will go if you send it to Midhurst for example.... this is not considered to be a problem and any ATCO who then uses track separation without locking the aircraft on it's heading would be daft. I use the roueting to centre fix as a matter of course when it is quiet and this has to be the most expeditous route for all concerned. Your BA crew may have been surprised purely by how early the route was given, ask any charter crew who operate late at night and "direct c-fix" is certainly more likely to be the norm.
Long live the centre fix ( wherever it may be !!!)
NsR