I think I'm going to revise the ideas a bit, this is all a little bit rushed:
Fi tells a person what they feel about their inner workings, and becomes a factor in the outer world when it is informed by other functions. The other functions, I guess the perceptions functions, tell the person what's going on outside them. The extraverted perception functions tell the person immediately. The introverted perception functions provide a backlog of understanding that can be drawn on to understand currently. Te provides truths. And all the functions are inter-related, sharing information.
Fe decides for the person what they feel immediately about the stuff outside them. It is a decision function, called upon immediately by outside events.
I'm getting lost here, no longer making sense. The core intuition for all of this is that Fe is analogous to Te, it makes decisions about what is right and wrong outside of the person, and it does so by directly affecting the user. It's not so much that they care about what's outside them, it's that the origin of the feeling literally resides in the things that happen outside the person. Just like for Te users the truth of things and processes literally resides in the reality of the things and processes that exist outside the person.
And the language for both Fi and Fe users is "I feel...", which makes the whole thing confusing to spell out. The trick would be to describe what it means to have the locus of feeling be i and inside the person or e and outside the person.