i see J vs P as general knowledge vs personal, experiential knowledge. Fe is different than Fi in that it's less in touch with the raw sensation of experience and more focused on the meaning of the gesture. it's more about the symbolism, what something "means" in terms of a form of expression situated within a social world. it's more rooted in the language of feeling than the internal experience of the feeling. the feeling in both cases passes through you, but Fe types are more drippy and saturated with feeling expressions in everything they do. they embody them, speak through them, take on the vocal inflections of them. they organize and re-organize themselves and their experience more through the process of embodying these outward forms rather than allowing their experiences to well up and take on whatever expression they and their process may take.
J processing is more top down. it guesses what things are by putting them in boxes, by dividing them into symbolic forms that center an idea of something. organizing categorically in order to understand what something is likely to mean universally rather than experienced particularly. P processing is more about rawness, what things are as they are, being aware of the information in a less filtered form. this is a central concept to me to understand the difference between Fe and Fi. they're both out there functioning as relationship management skill sets in social space. but they focus on different kinds of information, even as they both serve to bind together larger patterns of relationships into a felt, embodied, lived sense of the *self*. Fe focuses on ideas that reflect like mirrors the shape of the self as a representation rather than the thing itself directly, Fi focuses on the story of the experiencer as the center in which value can be discerned in relation to oneself as one truly is in that moment of the thing that continues until it doesn't any more.
as a result, Fe types are more predictive and guessing who they want to be. Fi types are more open to trying things and waiting to realize who they've become. in T types, the significance of the feeling function is often so much less that the difference between these processes can be obscured by the overwhelming force of the opposite orientation, of Te in tjs or Ti in tps. this obscures the ability to observe Fe/Fi at the level of the person's behavior as a whole, especially when it just gets to "adherence with norms" or not. this has more to do with instinctual subtype, as you note, when so types are more likely to allow others definitions of the situation to define the moment than their own. that's a level of attention that works at its own relative level and isn't reducible to Fe vs Fi. Fe and Fi could be called social ethics and personal ethics, but again the lines between those blur so much that it is more of an orientation rather than an easily divisable, tangibly different space with no overlap. the distinction is just not easy to make, because there's so many interrelated levels of analysis, and the systems are so dynamic that achieving a stable perspective to observe a single layer itself is kind of a work of art.