My understanding from my discussions over the years with TKV Desikachar regarding the context and content of Yoga Makaranda, is that when teaching youngsters the length of the breath was minimised to a relatively short fixed length and use of Kumbhaka was limited to a few seconds Antar Kumbhaka and Bahya Kumbhaka.
“The Āsana are presented in Vinyāsa Krama, the way it was taught to children in the Yogasāla.
This should not create the impression that T Krishnamacharya taught in this manner to everyone.”
– TKV Desikachar Introduction to Yoga Makaranda
In the adult there were no such limitations for the breath and the work with variations of the Āsana was re-prioritised to working with a fewer Āsana and fewer variations within each Āsana, but with the challenge of a greater range of breathing patterns both in length and combinations.
Certainly Antar Kumbhaka or Bahya Kumbhaka of 10″ was commonplace in the adult practice and here the ‘perfection’ of the Āsana was measured by mastery of all aspects of the breath rather than for the youngster, where ‘perfection’ of the Āsana was measured by mastery of all aspects of the form. This was consistent with Krishnamacharya’s teaching in his Yoga Rahasya on Yoga Sādhana and Stages of Life.
Furthermore my understanding is that if we use a particular Āsana with all its permutations of form and thus less focus on the variations of the breath it operates more as an Āsana. If we use a specific primary Āsana with the focus on all its permutations of breath and thus less priority around the variations of the form it operates more as a Mudrā.
Sarvaṅgāsana is such an example with its 32 variations devised by Krishnamacharya emphasising its role as an Āsana and its static solo form with its focus on extensive breath ratios involving all four aspects of the breath, perhaps augmented by the Tri Bandha, emphasising its role as a Mudrā.
For more on introduction to Yoga Makaranda read……
Introduction to the Yoga Makaranda by TKV Desikachar