[AntonioMQ]

I posted about this elsewhere just this morning; my understanding is that the sum total of sensory input from the body, when treated as a single percept, can then be distinguished according to whether or not any particular sensory impact is related to breathing, or not. A good example showcasing this is the difference between the sensory impact of the sitting surface versus the sensory impact of the abdomen during breathing (which itself is further distinguishable according to subtle differences between inhale and exhale functions, per steps 1 and 2).

Therefore, rather than thinking of the body in terms of gross anatomy (belly, lip, nose, foot), one takes the sum total of sensory impacts arising in the body, some of which are to do with breathing and some of which are not. Thereafter, the sensory impact of breathing is a 'body' within the larger context of the other sensory impacts, to wit "body among bodies".

Focusing on the breath moving past the lip or nostrils helps in the beginning perhaps, but the expansiveness of the four steps of Tetrad I altogether mean that nose-focus &tc. are a crutch, not a meditation object to become absorbed in. I think the commentarial literature makes missteps here.