A What/How/Why Model of Typology
I've come to this conclusion regarding both socionics and enneagram:
Enneatype (tritype, wings, etc.) = what you go after
Sociotype (and subtypes) = how you go after it
Instinctual stackings = why you go after it
There are obviously more harmonious and more tense combinations of these three, but as I see it now any combination is possible, not only the harmonious ones that people seem to assume are the only possible ones. I perceive the less harmonious/more tense ones as having sort of more dynamism to get things done externally since it's sort of pulled tighter, but also as being rougher to have from an internal perspective since there's all the tension on you.
I also have ideas about how enneatypes and instinctual stackings are derived from Reinin (including Jungian) dichotomies but that's complicated and not complete so I won't go into it here yet.