Something in my aging, decrepit brain just went click. In the link to the abm0 post he refers to Dr David Griesinger and bingo! that’s the guy. Here’s the YT vid, the demonstrations start just before minute 12: https://www.youtube.com/watch?v=a-JGAobDwGs. And that’s just a demonstration of ear canal variance. I can only imagine what happens when we add pinna and concha variations.