That heavily depends on translation and interpretation
From Satipatthana sutta translation by ven Nyanasatta
Just as a skillful turner or turner’s apprentice, making a long turn, knows, “I am making a long turn,” or making a short turn, knows, “I am making a short turn,” just so the monk, breathing in a long breath, knows, “I am breathing in a long breath”; breathing out a long breath, he knows, “I am breathing out a long breath”; breathing in a short breath, he knows, “I am breathing in a short breath”; breathing out a short breath, he knows, “I am breathing out a short breath.”
The keyword here is knows, which is not focusing on a physical part or feeling. It’s in the domain of knowing, which is related to memory. You know what your posture is without having to look, because of memory. This is argued by some EBT followers as the true meaning of Sati, referring to memory and not sensuality.
Ever mindful he breathes in, mindful he breathes out. Breathing in a long breath, he knows, “I am breathing in a long breath”; breathing out a long breath, he knows, “I am breathing out a long breath”; breathing in a short breath, he knows, “I am breathing in a short breath”; breathing out a short breath, he knows, “I am breathing out a short breath.”
This is important because the defilements are in the mind, not the body, specifically the defilements come up in memory. Hence “mindfulness to the fore” could mean bringing attention to memory and mental images.
The practice should decrease your defilements, from Satipatthana sutta:
Or his mindfulness is established with the thought: “The body exists,” to the extent necessary just for knowledge and mindfulness, and he lives detached, and clings to nothing in the world. Thus also, monks, a monk lives contemplating the body in the body.
Notice the practice should result in non-clinging
For note 8 and 9 Nyanasatta writes
- That is, only impersonal bodily processes exist, without a self, soul, spirit or abiding essence or substance. The corresponding phrase in the following contemplations should be understood accordingly.
- Detached from craving and wrong view.
So the practice should result in no-self which results in the suppression or uprooting of craving and wrong view.
In my opinion, simply focusing on physical sensation of breath in the nose has nothing to do with no-self and the defilements, and only results in tiring the mind.
I also find this note interesting since it’s the exact opposite of what is taught on Mahasi/Tong Vipassana retreats
The repetition of the phrases ‘contemplating the body in the body,’ ‘feelings in feelings,’ etc. is meant to impress upon the meditator the importance of remaining aware whether, in the sustained attention directed upon a single chosen object, one is still keeping to it, and has not strayed into the field of another contemplation. For instance, when contemplating any bodily process, a meditator may unwittingly be side-tracked into a consideration of his feelings connected with that bodily process. He should then be clearly aware that he has left his original subject, and is engaged in the contemplation of feeling.
I think this is important because if you’re focusing on how the mind knows the breath or any single object, then it’s a lot easier to catch images of sensual desires and other defilements arise, whereas if you’re focused on the physicality of the breath, you’re leaving your mind unguarded. If your attention moves to whatever new object arises, as per Mahashi/Tong noting instructions, then you’re once again allowing yourself to get distracted.
The Buddha said the 6 animals (i.e. 6 senses) need to be tied to a post, a single object, so that they can’t run in different directions. Focusing on the breath physical feeling is tying the animals/senses to another animal/sense, not a post. Changing your attention to whatever new object arises, as per Mahasi vipassana, is constantly changing your post.