Ah! Thankyou Zebra. As ever, we discover accurate detail bit by bit!
@zebras makes a totally sensible point about reflecting any wiggles in the listener’s hearing curve.
When I was first assessed some four decades ago, I knew already from my piano that I had a very weak spot just above C2, 1kHz.
This therefore did not show up in the clinic, but of course back then such finessed compensation wasn’t possible in a hearing aid, probably still isn’t.
Just to make an observation (I’m not an audiologist of course, but in sound recording), it may be that these details add to individual brand preferences: for example hearing aids will usually have a mechanical resonance somewhere in mid-band: that could either exaggerate or relieve a ‘dip’ dependent on whether there happens to be a match.
This is certainly the case with loudspeakers and room peculiarities.