This is how I perceive H2018 tuned headphones, but not H2019 tuned IEMs. I'm not sure why. This also happens to be a common anecdote on the internet.The bass and treble are most likely not emphasized at all in the Harman transfer function preference target.
I'm often reminded of something of a divergence trend that can be seen among different types of playback systems. Ones that are lower-SPL(and lower-attentiveness?) applications like car audio systems and home stereos vs. and others like studio and stage monitors. In my estimation this difference is pretty close to an equal-loudness differential EQ. Could it help explain pervasive playback EQ divergences to some extent?
Two very different targets in Sean Olive listening test were statistically tied. https://aes2.org/publications/elibrary-page/?id=22696
This might reflect the range HRTF variation like you rightfully bring up. OTOH is my SPL-driven speculation any less valid?
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