This is all very interesting. You all seem to be describing Fe as something on the inside, but which can't readily be seen always. That's how I see introverted functions, but I never expected to see extroverted functions hidden that way. In an introvert, the auxiliary is the primary way of interacting with and acting in the external world, but for INFJs, that process seems to be restrained by the introvertedness or by the shell of IxxJness.
It may be slightly different for INTJs, whose auxiliary allows them to act in the world without necessarily interacting with people - it may make using the auxiliary less threatening to introversion?
It's strange - I've entertained the possibility that I may be an INFJ, and a lot of it fits, particularly the use of Ti. But it's always the Fe auxiliary that makes me think it must be otherwise, because, based on my understanding of Fe, it's one of my least used functions. But they way you're all describing it, it almost sounds more like a FeFi hybrid.
When you read a description of Fe, how strongly do you relate to it? How do you see your Fe differing from Fi?