i think the point about flare heights in a tailwind is: it depends a lot on airport geography.
the FCOM is written with a relatively constant tailwind down to the ground in mind. this might not be the most occuring scenario but it is the most conservative approach as airbus would rather have a float than a hard landing as someone wrote. (how wise that is is another topic)
now it as has been commented at most airports there is a tendency for the wind to reduce substantially in the lowest 100ft. if this is the case you gain airspeed at a low level and therefore can land with a later flare.
now with all the examples we have had no one has cited an airport or actual tailwind numbers. no one has stated wind differences at low level their airports get. all this will surely influence flare height quite a bit.
to give two different examples:
- an airport somewhat surrounded by buildings or forest
- an airport on an island where the runway is nearly surrounded by ocean
that would make quite a difference regarding lower wind layers, wouldn't it?