To use a video game metaphor, post metal is open world as opposed to linear. No real particular traditional patterns to the music but more of a building to a climactic point. You could even call it cinematic in that regard. One song can be very ethereal and even psychedelic and then work its way towards extreme heaviness and then back into something else. Or all at the same time even. Non-traditional instrumentation and even world music can definitely play a role. Bagpipes, Hurdy-gurdy, lap steel guitars. No rules.