I focus now on bigger area from top of the nose to upper lip.When I watch breath my focus goes from upper lip to nasal passage but could not return to upper lip that is my tiny spot of focus .It gets stucked up to nostril or base of nose.So what should I do to focus continuously upper lip to top of nose and return back from top of nose to upper lip.
In the words of the Buddha, "pari-mukham satim" (step 0.5) in the sutta: http://lucid24.org/sn/sn54/sn54-003/toc-addon/index.html
Translated literally means somewhere near the mouth area. In the vinaya, pari-mukham can refer to chest hair area, facial hair, so if you take the physical interpretation of that phrase, it's not exact, and most people translate it in physical spatial terms as "in front".
There's also figurative a meaning, "pari-mukham" meaning to make that that main priority, the main task. Just like in the English expression, "focusing on the task at hand". It doesn't literally mean the spatial location of your hands.
So the answer to your question is, it doesn't really matter exactly where near the mouth you focus. 16 APS anapana isn't about that. The point is to use the breath as a way to fill up the entire bandwidth of your attention so you stop unprofitable thinking, and then thinking itself (mental talk). Using the mouth area as a spatial focal point is just a suggested preliminary way to achieve that. The important part of 16 APS is to develop a calm, lucid state of mind that uses the pleasurable experience of attending fully to the tactile experience of breath sensation pervading the body as a natural incentive. It's easy to enter samadhi when the mind is happy and occupied. And the mind is much happier when it doesn't feel constricted, stuffed into a tiny box.
You can try the following to continuously focus on the upper lip:
- Concern - one should be concerned to retain the object of meditation may it be breath or metta
- Reaction - one should see if one's mind is with the object and if not bring it back. Even if not periodically are apply your mind to the objects by trying to see the meditation object (in the case the upper lip) or be with the meditation object.
- Attention - one should pay attention to what the mind is doing, i.e., wandering off or staying in focus
- Reviewing - periodically are checking if you are at the chosen place
Having said this:
- When the area is bigger there is a chance you can feel the touch better
- When the area is small one has to concentrate more, hence doing so increases concentration
So if your concentration is weak to be at the upper lip where the feeling of the breath is the very subtle increase the area to include the tip of the nose or even the top of the nose.