That's a really interesting observation and question. This is kind of how I see it:i'm not sure but so far with my intj 6 i've encountered a huuuuge difference in tertiary Fi vs Ti. she wants something comforting and nostalgic akin to an inner child that too often gets left behind (Te!) and just wants to play. whereas i use it to break things apart, analyze them until i feel i have total mastery over them as a discourse, that my understanding and its corresponding articulation are perfected, that i have perfectly precisely (and somewhat detachedly) synthesized the Fe values present around me, in my awareness and attention, circulating throughout the social game as pertains to my position within it.
i'm wondering how this would work for an infj 6? how the motivations would be processed via cognitive functions and what it would look like?
1. Every Ni is going to imagine Something Better.
2. For most people, Something Better is something obviously more. More education, more money, more travel, more opportunities...
3. With "more," usually comes change (travel means leaving home, money means moving to a bigger house, etc...)
4. Type 6 wants security - not so big on change
5. So, the Something Better that the Ni projects for a Type 6 can actually seem like something less. The mundane is romanticized. Monotony is the end goal, but it never quite exists in the present.
As for the auxiliary function, I think Type 6 and Fe are very compatible: we want to be accepted, so we learn to be socially acceptable.
My tertiary Ti actually sounds a lot like what you describe. I'm very analytical, and every person or situation gets filtered into a web of theories (that I spend an embarrassing amount of time crafting). That mental grid of theories is actually pretty reliable (which can make me come across as cynical from time to time... like I have people "figured out" before I give them a chance), but obviously it's never 100%. Some people surprise me. Some don't fit in with any of the archetypes I've set up. That leads to a kind of push-pull I have: I'm drawn to those surprises, but I'm very reluctant to alter the carefully crafted system (classic Ni vs. Ne, I guess). I think it's exacerbated in Type 6 though because the system itself provides added security.
Sorry for the point-by-point answer (my love of these point-by-point responses is one of the main reasons I haven't closed the door on the possibility I'm an INTJ )