As Pa Auk Sayadaw would say -
this is exactly what happens when people don’t read the Commentaries.
But in fact, you don’t have to read Commentaries. Just read Abhidhamma, the original main text.
‘‘Parimukhaṃ satiṃ upaṭṭhapetvā’’ti tattha katamā sati? Yā sati anussati paṭissati…pe… sammāsati – ayaṃ vuccati ‘‘sati’’. Ayaṃ sati upaṭṭhitā hoti supaṭṭhitā nāsikagge vā mukhanimitte vā. Tena vuccati ‘‘parimukhaṃ satiṃ upaṭṭhapetvā’’ti. (Abhidhamma - Vibhanga 2. Jhānavibhaṅgo - Mātikā - Par.537)
It means that keeping attention at parimukha means being mindful of breath either at the tip of the nose or at the sign of mouth. The Commentaries explain that long-nosed people keep attention at the tip of the nose (apparently “looking” at the nose, without closing eyes, as we see e.g., in the Priest King statue from ancient times.) Those who have a short nose have to “imagine” (hence “sign,” nimitta) their upper lip and concentrate on that.
Again, this is not Commentary, it is from the main scripture, Abhidhamma.
The book Patisambhidamagga (which is officially included in the main text of Tipitaka and has its own Commentary) also mentions that “parimukhaṃ satiṃ upaṭṭhapetvā” consists of three portions -
“Parīti pariggahaṭṭho. Mukhanti niyyānaṭṭho. Satīti upaṭṭhānaṭṭho. Tena vuccati – ‘‘parimukhaṃ satiṃ upaṭṭhapetvā’’ti.”
“Established mindfulness in front of him (parimukhaṃ satiṃ upaṭṭhapetvā) : pari has the sense of embracing; mukhaṃ (lit. mouth) has the sense of outlet; sati (mindfulness) has the sense of establishment (foundation). Hence 'parimukhaṃ satiṃ upaṭṭhapetvā ‘established mindfulness in front of him’ is said.(Footnote 14)”
(Endnote no.14) “‘Has the sense of embracing’ is in the sense of being embraced. What is embraced? The outlet. What outlet? Concentration based on mindfulness of breathing is itself the outlet, right up to the arahant path. Hence ‘has the sense of outlet’ is said. The meaning of ‘outlet from the round of rebirths’ is expressed by the meaning of the word mukha (mouth) as foremost (front). ‘Has the sense of establishing’ is in the sense of individual essence. The meaning expressed by all these words is: Having made mindfulness an embraced outlet. But some say that ‘has the sense of embracing’ stands for ‘embracing as the meaning of mindfulness’, and that ‘has the sense of outlet’ stands for ‘door of entry and exit as the meaning of in-breaths and out-breaths’. Then what is meant is: Having established mindfulness as the embraced outlet of the in-breaths and out-breaths’ (PsA 350-1)”
(Copied from Paṭisambhidāmagga, The Path of Discrimination, translation by venerable Ñāṇamoli, p.177 and note 14 from p.206)
The Buddha however didn’t teach just observing the breath for concentration on the body, but also observing one’s postures, actions, 32 parts of the physical body, and four elements. The fact that anapanassati is “breath” and not kusalā akusalā dhammā (skillful and unskillful phenomena) is clear from the fact that this practice is included in the Kāyānupassanā chapter of Satipaṭṭhāna Sutta. Kāyānupassanā means observing the body. (Skillful and unskillful is then to be observed as practices in Dhammānupassanā, e.g., in observing the six senses and sense-objects mentioned in the Ayatanapabba sub-chapter of Satipatthana Sutta).
But you don’t need to concentrate on the breath to attain Enlightenment. There are nine other options for you. Including breath, each of the ten is “the one thing” that can take you to Enlightenment. See them here - SuttaCentral .