Hi Dirk,
On first place - forget about “transversal velocity”. That term was coined to simplify the explanation, but actually made it more complicated… As is current “tracking” stat for turrets.
Formula is not changed (in the part concerning ranges), but tooltip has changed several times for the short period since it was introduced. I failed to find your
but my wild guess is you refer to Quad Anode Light Particle Stream I. I tried to mount it on Gnosis (another wild guess) and with perfect gunnery skills I found following tooltip:
Falloff range within 12 km
Optimal range within 11 km
When I apply Microwave M numbers change to:
Falloff range within 17 km
Optimal range within 16 km
So if you are not far with gunnery skills it is quite possible to have your numbers around 14-15 km. And that is what you observe during your tests.
At this point either you consider me a total idiot, or you already are looking at info panel at your weapon where it says (without Microwave lenses):
Optimal range ~11 km and Accuracy falloff ~ 1000 m
Moral of the story - on tooltip Falloff range within xx km measures Optimal + Falloff. 
Mystery solved?