Does the "whole body" in the sutta refer to the whole breath (body) from start to end or experiencing the breath in the whole (physical) body? As I try to read more on this, I just keep on coming across bhikkhus saying the one or the other or both. So I am thinking of trying the different approaches and see what works for me.
Replying from phone, so excuse the brevity...
I tried out both. Nothing wrong with some experimentation. But in retrospect, I think we already cover knowing the breath from beginning to end, with step 2.
Ultimately, I settled on kind of expanding awareness into my entire physical body, and observing this body sitting here, breathing in, and breathing out. The jhana similes' imagery, afaics, all point to jhana as a whole-body experience. Not limited to one little spot, but rather, permeating every bit of one's body. So if this is where we are headed, maybe that third step, by having us train the mind to be sensitive to the entire body while breathing, conveniently prepares us for what is to come later on.