Jeff after re-reading Rics description, and your thoughts, you may indeed be better tuned to the explanation suggested.
Viewing the kite photo, the light blue ocean starts half way up the groove zone. It doesn't get deep blue until the end of the spur and groove area..
So it could very well be the second half of the spur area is the area of 20 foot water, dropping to 60 foot water.
The first cliff could well be the end of the spur and groove area where Ric says it drops another 200 feet down to the 300 foot range.
300+ feet of water would fit nicely with the dark blue water shown just after the spur area.
Given that, then any spotting of wreckage would have to be before the first cliff, and indeed on the spur and groove section of reef. In fact, I think you are right in that Ric is referring to part of the spur and groove area as the unmapped area too dangerous to explore.
But that presents a problem, and you touched on it with Emily's description. Reading her words indicates to me she was describing rusty beam steel laying exposed at certain times of tide. Well that could not occur in 20 foot of water. If she was describing a wing sticking up, or a tail sticking up, then the majority of the attached superstructure could be in 20 feet of water.
However, It seems like she is describing something laying visible and relatively flat, a long rusty straight beam laying on rock quite exposed.
That would either be on the reef flat itself, or the first section of the spur and groove area. That would be quite shallow at times, perhaps a foot or three. A plane Fuselage wouldn't be hidden at any time in a foot or two of water at low tide.
So reading her description again sounds increasingly like norwich wreckage laying on the reef, in very shallow water less than 10 feet certainly, and not in the 20-80 foot unmapped area.
At least that is the way I read her testimony.
Again, it doesn't mean there wasn't a plane even in 60 foot of water occassionally depositing a wing or skin.
It just means that from Emily's description she wasnt seeing huge sections of aircraft, or aircraft at all since she talks of beams laying on rock. That all sounds very Norwich.