You're certainly not alone in your broken record-ness about this. Aargh, especially when the majority of the fic that exists is based entirely on FotH and uses at most a few background details from the other two books—GitN fic would be a different thing!

At least 'Flight of the Heron - D. K. Broster' is still synned to the canonical tag, so one can at least tag one's own fic accurately, even if only as a symbolic gesture. Perhaps I take this too seriously...!