Rambler.
I'll try and explain
The ghost anagram works as follows.
Regular cryptic clue is:
Cheap kind of fruit (5) - ANSWER = PEACH
Cheap = anagram fodder
kind of = anagram indicator
fruit = Definition
The Ghost works as follows:
Inexpensive kind of fruit (5)
Fruit remains the Definition
kind of remains the anagram indicator
BUT
Inexpensive is NOT the anagram fodder (and not the wordplay) but a synonym of the word that has to be found before one can create an anagram from it (the wordplay).
So it's like the cryptic wordplay is once removed from the original fair play of the clue
So, where you used KEEN, then that has to be associated (or synonymised) with Eager/Eagre to then be synonymised with TIDAL BORE which is once removed from what should be the original fair wordplay of the clue.
So aristo's ABC is a good bench mark to go by because A associated with B is fair and B associated with C would be also fair (I think) but A is not associated with C directly so is once removed from the clue and would be deemed unfair.
Did all that make sense, I think I confused myself somewhere in there.
NB: I have no idea if 'synonymised' is actually a word without checking... Ha ha!