PariMukkhaṃ Satiṃ upaṭṭhapetvā = the practitioner focuses the mindfulness on only Breaths.
So satova assasati satova passasati = he is focusing the mindfulness like that and breathing out/in.
Breaths are not nose tip, touching, or feeling. Breaths are long or short wind flowing at nose tip.
Sometime breaths appear at right nostril tip, sometime left, sometime middle, some time top lip.
But you are focus on clearing appearing breaths at somewhere of those, so wherever of them is OK.
The other touching points such as in side the nose or lung is over width for clear focusing on breath and easily to get Restlessness (uddhacca), so appearing breaths on somewhere at the nose tip is the best choice for the meditation.
