I just tried F-Akiha's bunker in training mode, and it is clearly not air techable.
edit: I did some more testing and its not just Akiha. For the C/F moons:
Akiha, VAkiha, Kohaku have bunkers with untechable knockdown.
Satsuki, Arc, Warc, Ryougi have bunkers that can only be ground teched.
Aoko, Kouma, Roa, Hisui, SAkiha have bunkers that wallslam so they are air untechable when close to the corner (but ground techable).
So probably for CC they've made C/F bunkers universally air techable