You said"classical guitar posture"
well those people are very rigid in their rules.
The flamenco traditionalists are the same rigid.
But every now and then, somebody comes along and plays the most wonderful guitar, in a new position, their position, a new way, and as long as it sounds great, who cares how you get your sound across?
Watch Paco de Lucia on u tube, see his position, that is his own, which a lot copy now, and he got a lot of complaints from the traditionalists for that, yet he is a legend as was jimi hendrix, who even used his teeth, but thats another world.