It depends on the situation. There are two threads right now about Fi and Fe users explaining how they experience their feeling functions. I read the posts, pick out things from each post that fit me or don't, and assess the person's writing style. As an example. Also I pay attention to and ask questions about the types and certain things, like whether a behavior/feeling/characteristic fits more with one type or function than another, or to see if it is indeed correlated with type. Depending on whether that thing is true of me, I can use that as a piece of "evidence" to point me to a type. 50 such things pointing to one type versus 20 things pointing to another type, and taking into account prominence of said thing in type, I can decide at any moment whether I think the "evidence" points overwhelmingly toward one type or another.
Yes, those 3 are the consensus at the moment. INTJ does a good job of balancing the opposing dominant functions with Ni; and if I think I am more INTX than INXP, I can say that Fi and (developed) Te from INFP fit nicely into INTJ to balance the opposing T functions with the help of Ni/Ne. The INTX part of the theory isn't completely clear yet.
This is part of my Intertype Fluidity Theory, which uses CF interaction to account for type variation and ambiguity.