I watched the TPE subtype theory video and latched onto something you mentioned in this slide: that Aushra considered the third function to be vulnerable rather than the fourth.



To put that in perspective I made notes. I wanted to visualise how it forms a duality, or conflict, between types. (please let me know if I've misconstrued function strength)

LSI
Fe suggestive; as their vulnerable/blindspot is Fi (3rd fx)
Consciously(?) ignores Ne, and they are mobilised by Ni

LIE
Fi suggestive, blindspot Fe
Ignoring Si, mobilised by Se

SEE
Ni suggestive, Blindspot Ne
Ignoring Ti (LII conflict), mobilised by Te

SEI
Ne suggestive, Blindspot Ni
Ignoring Te, mobilised by Ti

SLE
Ni suggestive, Blindspot Ne
Ignoring Fi, mobilised by Fe

Our dual type has as their leading function either the Energy metabolism (EM) or the Information Metabolism (IM) we are "missing". That is, our blindspot/vulnerable function.
EM and IM exist as pairs; Fe and Fi, dynamic and static. It is better described in your model A article:

As I understand Aushra paired two different elements in the model also because it gives the person a better (more objective) understanding of the world around him (reality) as one element of IM is continuity of another.
She also refers to Jung by saying that one block (a pair of functions) in the model A starts with the body-tact and finishes with the field-tact. In this block extraverted information about the state/quality of object transfers into the information about relation of one object to another. That is what is inside the object is transferred into the external world – according to Jung “becomes extraverted.”

I would be interested in reading snippets of your book, yes