I also want to know what the reason is behind "dynamics". Andrew Park over at The Headphone Show also calls this phenomenon "macro-contrast".
When I compare the Focal Clear MG and the Hifiman HE-500, Sennheiser HD600, or basically any other headphone I have, the Clear MG always comes out on top with the most hard hitting and quick response. It feels like the sound is more violently being pushed into your ears, like the sound is somehow being pushed faster and harder. It's not just one part of the frequency response, every part of the mix pops out more, whether that's the bass, mids, or treble. People have speculated this dynamic behavior can be found in normal FR graphs, but I'm not so sure. Maybe impulse response and CSD graphs can help figure it out, but that's just speculation on my part. It could also be how good of a seal you get, even with open headphones, that affects dynamics.