meditation - How obvious should the touch of the breath be?

When I try to feel the sensations of the breath at the nostrils/upper lip during anapana, it's so faint that after a certain point, I think I may be imagining the touch of the breath. I may even feel other sensations (pressure/vibrations) on my face but I would still have trouble feeling the touch of my breath at the rims of my nostrils or my upper lip. And my mind is still very much lost in thought so I know it's not because I've become very concentrated or anything. So how obvious should the touch of the breath be? Should it be as faint/subtle to the point of almost feeling imaginary? Should I stick to this and assume it will approve as does my concentration?