What does post-metal even mean, in the context of this band?
Isn't that kind of what Disambiguation was?
The only band I've ever heard with that term associated to it is Russian Circles.
Russian Circles, ISIS, Mono, Pelican, Rosetta, etc etc.
It's a pretty vast genre. I'd agree that a lot of the ambient, droning parts of the music of the last two would fit the genre. Obviously they have more vocals that the rest. People call Moving Mountains post-rock even though they're full of vocals as well.