Yea, I'd be interested in where Fi-9s differ from Fe-9s, simply put. roud: The Timeless articles barely go into any Detail f.e.
I am an ENFP 9w8 and I related strongly with the second paragraph. I wonder if having Fi and Te in our cognitive stack makes our w8 heavier. Due to my Fi I can easily discern what I DON'T want and rise my voice accordingly. My Te would represent the bluntness of my w8.ISFJ husband is a 9w1. I think as a Fe-aux 9, he uses Fe to set strong personal boundaries that create/protect calm. He makes it clear where others stand with him. He can be quite animated and engaging socially, but also needs substantial alone time. He removes himself from external disharmony more often than trying to change it. He is not always strong with identifying and vocalizing his feelings. He doesn't really seem to merge much with others; he's sx-last. He seems to merge more with interests and activities, especially music. He likes both routine and independence - he likes being the captain of his ship - but is not very interested in controlling his environment. He just wants to be able to do what he wants to do when he wants to do it. He is generally disinterested in determining that for others.
My cousin in contrast - I believe she's an ESFP 9w8. She's very casual, happy-go-lucky, but also can be a loud and surprisingly commanding force at times. She has to have sx higher in her stack, maybe even first, sx/soc. She is very much the peacemaker. She wears her heart on her sleeve more, and is more open to being offensive - even though she prefers everyone to get along. In contrast with my ISFJ 9, she generally doesn't lay down boundaries until someone goes too far - then she makes them very clear. She seems to have a very clear picture of what she feels. She seems to merge more with others, but also merges more strongly with interests and activities. She's a bit of a thrill-seeker. She is more "wide open" but her energy fluctuates more than my ISFJ's. His is very steady. Hers varies widely with her engagement in a topic/activity.
Dissociate is an excellent word for it. Yes, I'm an infp 9 like your mom and I can more or less choose how affected I wanted to be by the emotions of those around me, it's like having an internal wall. I see fe as being more fluid, and fi as more rigid and selective.My mom is an INFP 9 and I am a (likely) INFJ 9.
My mom has a pretty clear awareness of her feelings, while I do not. When something happens, she is able to pinpoint how that makes her feel, if she likes it, what she wants to do, etc. You get a strong "I'm in touch with my feelings" vibe from talking to her - here are some things she might say or do to kind of show what I mean: not being able to go see a certain movie because it might be sad, talking a lot about something she saw that was really cute or funny and why it was important, being stubbornly persistent about something she really wants (Honestly in contrast this makes Fe 9s sound like we have no personality, but sometimes it can feel like that, sadly). All of these things incite some kind of internal, emotional reaction in Fi 9.
I am not like my mom in that way. I pick off the feelings of others and it helps me decide what I'm probably feeling, or what I should be feeling in a given situation. Sometimes I feel lost or empty/apathetic if I don't have access to external feelings. It's not easy for me to see how something is affecting me. There are exceptions to this (such as after I've suppressed my emotions so much they start to come out in a storm, but that's another topic entirely), but as a general rule this is the case. It's also relatively simple for me to be "persuaded" by other people's emotions and totally shift my mood to match theirs. I can be affected by different things like movies, music, etc. but I almost always need an outlet (i.e. another person) to kind of share it with. My emotions, facial expressions, etc. will then start to become more animated and lively... but I 100% need that outlet.
I think there is something to Fi wanting internal harmony, but Fe does too... it's just that Fe's internal harmony is perhaps affected more by the external harmony. An Fe 9 will not feel at peace if what's around her is tense. I don't want to try to speak for an Fi 9, but from observing my mom, I can say she has a decent ability to dissociate from other people's emotions in order to keep her peace of mind. I will dissociate too in difficult situations, but moreso from my own emotions.