I have at times been accused of being against JCF. In fact, I am not. In fact, lately I have been studying Jung's original cognitive types more intently than usual.
Modern JCF theory is dominated by the unwarranted assumption that MBTI types are created from combinations of Jung's dominant and auxiliary types. Thus:
ISFJ = Si + Fe; ISTJ = Si + Te;
ESFJ = Fe + Si; ESTJ = Te + Si;
INFP = Fi + Ne; INTP = Ti + Ne;
ENFP = Ne + Fi; ENTP = Ne + Ti;...
...and so on.
Notice, however, that in the first two rows of types, Si, whether as dominant or when relegated to the role of auxiliary, is never part of a Perceptive type but only a Judging type. By the same token, Ne, in the second group, is always part of a Perceptive type, but never a Judging type, even when in the auxiliary position.
Now if P and J are determined, not by some function-order formula considered valid only by assumption, but originally in Myers-Briggs' terms, as personality categories in their own right, then there is no reason why we can't have an "ISFJ" (in JCF terms, note the scare-quotes) who is, externally, a Perceiver.
P and J were originally conceived by Myers and Briggs to be externalized components of personality. Does the person generally, for the most part, appear to be: A. Spontaneous, or B. Controlling? A. Fun-loving, or B. Work-oriented?
Seen in the light of original MBTI theory, JCF quickly falls apart. The Si dominant and auxiliary types can no longer only be considered, controlling, work-oriented J personalities. The possibility is opened up for Si dominant and auxiliary types to be spontaneous and fun-loving.
Ne types, whether dominant or auxiliary, are no longer considered just part of spontaneous, fun-loving P personality types; they can also be controlling and work-oriented J types.
So contrary to JCF stereotypes about dominant and auxiliary functions:
Ni and Si people can have spontaneous and fun-loving personalities.
Fi and Ti people can have controlling and work-oriented personalities.
Fe and Te people can have spontaneous and fun-loving personalities.
Ne and Se people can have controlling and work-oriented personalities.