For anyone who wishes to practice mindfulness of breathing as described in the Anapanasati Sutta (M. iii. 78–79) it is almost impossible to make any sense of the underpinnings of the practice especially with regard to the preliminary instruction of "placing mindfulness in front of him" (P., parimukham satim upatthahanto). Indeed, this one passage can be taken in so many ways it boggles the mind.
The source of the problem points to the word, "mukha" which has a number of definitions/synonyms such as the following: mouth, opening aperture, entrance into or egress out, the fore part, front, head, chief, principle, best, beginning, source, cause, occasion of, a means, the original cause or source of the action, etc.
Next, when we marry the prefix pari to mukha (in Sanskrit it would probably be prati-mukha) the meaning becomes even more troublesome to untangle as it applies specifically to meditation.
The old Pali commentaries which try to explain the recondite term, “mukha” including “pari” by giving us a number of choices fares no better. To be sure, the proper notion seems altogether lacking. And some renderings of parimukha such as "around the mouth" are perhaps too literal. For example, being around-the-mouth-mindful (parimukhasati) doesn't seem to work within the framework of the Satipatthana Sutta when applied to overcoming mental disturbances (nivârana) or accessing the divine abodes.
My own reading of the term parimukham satim leans strongly to the notion that attending to the body by way of being aware or mindful (sati/smriti) means being antecedent or anterior to the body’s workings both physical and mental. In short, this is the development of detachment. A fair rendering of parimukham satim upatthahanto might read, setting up mindfulness antecedently or in terms of the entire body itself, to be prior to it, including its respiration.
It seems logical that mentally following the breath ties one to the finite body. This makes little or no sense since our attention is being given to a temporal condition not a transcendent one such as nirvana. The Buddha, in fact, calls in-breathing and out-breathing an activity of the body (M. i. 301) and speaks of stopping (nirodha) the activity of the body—not following it. If we are potentially not subject to birth and death since we possess the Buddha-nature or Tathagata potentiality, why must we follow the breath by focusing on the mouth, lip, or the nose? The right direction to take is one that makes us look at the body from an incorporeal perspective.
Instead of following the breath, we should set up our meditation so as to place our attention (sati/smriti) before or around (pari) the entire body in which respiration is but a part of it. Regarding this, it is noteworthy that the Pali Text Society’s Pali-English Dictionary translates “parimukham satim upatthapetum” with “to surround oneself with watchfulness of mind” (672).
Incidentally, I have meditated this way for years the result being that eventually there is established a clear distinction between my awareness (sati/smriti) and the mortal body. And I agree with the Buddha who said of this particular meditation that one “develops the link in awakening that is mindfulness and is dependent on aloofness, dependent on detachment, dependent on cessation and abandoning...the link in awakening that is energy...is rapture...”(M. iii. 88).