Probably my best-sustained effort at really getting the physicality of a character on the page is Dead Rick in With Fate Conspire; I have no idea how much that's due to me having a firm casting for him before I even started writing the book (Burn Gorman, owing a lot to his Torchwood role)

That's neat. Do you usually cast your characters?

a movement that would be a sneer if he let it go further.

See, I think there is nothing wrong with that description at all: it signals emotion, potential, movement, restraint. It's much more evocative to me than either of the two—admittedly inadequate—suggestions you offer in quotes.