This isn't exactly related, but I have my own spanners to toss around. I think the system is kind of botched to begin with, especially when it comes to IPs and IJs. If you read Myers' book, she explicitly redefined what Fi and Ti dominants even are (relative to Jung). People criticize Socionics as having strange function definitions, but it's actually closer to Jung than MBTI.
It might be easier to deduce that you're an ISFp there (whether that's ISFP or ISFJ here is something that's been confusing me..).
But at the end of the day, it doesn't matter either. Don't think about it too much.