Glad you like it!
I came up with all of this after a whole year of experimenting, failing, and experimenting again with the ES10.
Owning the ES10, I realized it was just the perfect statement headphone for me... since:
1) It's not hard to drive at all, and pretty much anything can make them it loud enough
2) It's a super portable headphone with massive drivers, the only one of its kind IMO
3) The tuning was close to ideal already. It just needed the extra push.
So that "extra push" lead me to experiment endlessly to improve on what it's missing (mainly just clarity and treble extension) while keeping what's already there (the strong bass, the warm and lush mid).
I do use a bit of physics to go about this. It's not that I blindly followed everything without a concrete base.
For instance, the sides of the ear cups would reflect more high frequencies (especially the top) because only those kinds can get past the enclosure and reach those regions. In order to improve them, a reflective surface such as the aluminum foil in dynamat would help. Plus the glue in dynamat has good elasticity, so it'll be pretty good at cleaning up extra vibrations from the cup, thus adding more clarity.
The back of the driver enclosure, which is open, would have sound output of various frequencies, but lower frequencies... from sub bass to mids would dominate higher ones there, so dampening that part would affect bass and midrange more.
Leather and felt are chosen for the task because they are not too stiff and not too soft. Stiffer materials would be more rigid, so they would tend to dampen higher frequencies more, and may make midrange too muffled, though they would help with bass. But we won't be needing more bass because... the construction of the ES10 allows quite a bit of air to get in already. Having those holes help ensure a pressure difference between the two sides of the drivers, and then they push more pressure, which makes more bass. Having more open space (less material) would then allow the bass to come out like that. Additionally, having more dampening materials in the back would cause them to stiffen, and they'll also transfer low frequency energy from the driver enclosure to the ear cups better. That's why Audio Technica compressed the yellow fiberglass material to begin with.
Finally, the wool felt and foam pieces at the bottom quarter help dampen extra vibrations from the cable, and also help dampen reflections coming from that quarter, which can be complicated because the cable is mixed in. Having them there aids in clarity and reduces a bit of bass warmth so that bass can come across clean and without intruding into the mids.