The way I see it the first four lines (1-4) refer to the first (30%) of the path to the first jhana. The next 4 (5-8) refer to the middle (30%), by the end of which you will completed 2/3 of the way there. The 9-12 steps is the last 30%, by the end of which you are in the first jhana.
Long breath, short breath, whole body of breath, stopping of the breath-30%
Piti, sukha, mental fabrication, calming mental fabrication -60%
Sensitive/experiencing the mind, gladdening the mind,unifying the mind, releasing the mind (first jhana) -100%
It is a very sophisticated way of doing anapanasati- I only realised this many years after I actually went past these stages in a 'rough and ready' way. It is well worthwhile following the steps and seeing where it takes you.