Is observing the start-middle-end of breath a correct practice in Anapanasati meditation? I was reading through Patisambhidamagga, KN. From page 164, it describes about 'Eighteen kinds of knowledge of imperfections' related to Anapanasati(Mahavagga-&gt;Anapanasatikatha).
Following is the except:

1)When he goes in with mindfulness after the beginning, middle and end of the in-breath, his cognizance being distracted internally, both his body and his cognizance are disquieted, perturbed and excited.
2)When he goes out with mindfulness after the beginning, middle and end of the out-breath, his cognizance being distracted internally, both his body and his cognizance are disquieted, perturbed and excited.
3)With such behavior of craving as hope for, and attachment to, in-breath both his body and his cognizance are disquieted, perturbed and excited.
4)With such behavior of craving as hope for, and attachment to, out-breath both his body and his cognizance are disquieted, perturbed and excited.
5)Owing to longing for out-breath in him when he is fatigued by [too long or too short] in-breath is body..
....

Does anybody have a reference to pali canon(not commentary) where it supports the observation of start-middle-end of breath?
He trains himself thus: "I shall breathe in experiencing the whole body (of breath)",
  
  He trains himself thus: "I shall breathe out experiencing the whole body (of breath)",
  
  ...
  
  Just as a skilled turner or his apprentice, when making a long turn, understands that he is making
  a long turn, or in making a short turn, understands that he is making a short turn, so, too, a monk
  
  ...
  
  He trains himself thus: "I shall breathe in experiencing the whole body (of breath)",
  
  He trains himself thus: "I shall breathe out experiencing the whole body (of breath)",


Source: Mahā Sati’patthāna Sutta

Experiencing the whole breath is sometimes interpreted as being aware of the start-middle-end of the breath. Also the skilled tuner passage seems to imply such as cited by some in support of this interpretation.

See: How is the Pali Phase &quot;Sabbakayapatisamvedi Assasissami... passasissamiti sikkhati...&quot; Interpreted as per Different Linage?