I currently have reservations about whether use of the 5128 will show us much about the 5-12kHz area though (although I would love to be proved otherwise).
I think this comes back to your question of what is 'reality'.
Here is the Twitter thread from Dr. Olive with examples of blocked canal measurements which most of us have seen before.
View attachment 284160
For the sake of another data point, here's my HD6XX on my FPC and in ear mic.
The frequency response in each person's ear above 5khz is all over the place and there are enormous variations between subjects.
Is there anything wrong with this though? Is it due to the headphone design or are we just seeing the response of each person's ear in a way that would be representative of any other input, e.g. sound coming from speakers? If this were so, are some headphones better at matching this than others? Does it tell us anything about perception or preference anyway?
Sorry if this doesn't make sense, finding it hard to verbalize my thoughts so posing questions was the best way I can do it right now.
I hope this make sense though? I guess I see a paradox arising where, in order to demonstrate meaningful results in the treble, you'd have to make a target curve with very little smoothing so you can see all the interesting peaks and dips. But then as soon as you've done that you've just created a target which doesn't match most people. So you have to smooth it more and more until it isn't miles away from the average of what most people hear anyway.
I re-watched Amir's old video on
understanding headphone measurements and that helps to understand where he's coming from in this discussion. "You have to allow for a certain amount of uncertainty. Nothing about headphone analysis or even equalisation should be about precise assessments".