I've been working on highly detailed illustrations of the A330/340 family, and have come across something slightly puzzling. Most A330s and A340s have a much smaller fairing at the base of the vertical fin than a few others. What tipped me off to this was looking at photos of a Singapore A340-313E. The fairing is much larger than other A340s, but not as large as that on the A340-500/600.
I've downloaded a ton of technical information in the documents Airbus has available (station diagrams, etc), but this is not addressed in any of them.
Can anyone intimately familiar with the Airbus family shed any light on it? What fairing goes with which type(s), and what the difference is?