My J/P is very much in the middle, but I relate to the cognitive functions and archetype of INFJ far more than INFP. There are a lot of subtle differences between the two, and I also line up with INFJ on those. It's the generalized differences in which I'm more ambiguous. I may not appear structured and I question the validity of all rules, but if you took a closer look at how I live my life the subtleties would tell a different story. I used to be a terrible student and would procrastinate and only do what I felt like, but I hated myself for it and I'm far happier now. I still don't get everything done. So I come down more on the side of J and P being more of a continuum than a dichotomy, but I believe the cognitive functions make a lot of sense too.
J characteristics which apply to me:
-synthetic thinker: if given a bunch of information I will immediately try to find a unifying theme.
-love planning, love organization of tangible objects, love preparation
-try to keep converations on topic
-like to limit my intake of information
-value external and collective standards
-set goals for myself
-am organized and my belongings are neat, aside from some piles of papers or clothes or random junk I don't want to deal with atm
-change my mind and don't follow my own plans if I don't feel like it
-generally think it's not my business to influence or control other people
-don't try to control the external world
-think informing people is better than directing them
-comfortable with not knowing the answers, but always like to have opinions
-I pay attention to time and it makes me anxious, but not always, and I don't have a good understanding of it. I tend to think I have infinite time to do everything, and even though I generally do things quickly I get distracted with other things.
So based on these it's not immediately clear I'm an INFJ probably. When I read description of J/P I could say both sets apply to me. I prefer to be a J but I'm sometimes not goot at it.