Looking at the 4 letters in my type, INTJ:
I have a fairly strong sense of being more introverted than extroverted, more intuitive than sensing and more thinking than feeling.
However, don't idenitify strongly with being more judgemental than perceptive. Originally I thought I was P. I started to suspect I might be J mostly based on the function order. I feel that NiTe describes me much better than TiNe, which would make me INTJ. Several tests I have taken on line score me as INTJ.
Most of the things I have read that talk about the letters individually tends to focus on S, N, T and F or Si, Se, Ni, Ne, Ti, Te, Fi, Fe. They don't really talk as much about J and P. I have read things on how to tell Ni from Ne but nothing on NP v. NJ. It sound like Keirnsey talks about J v. P, but only for people who are S.
So are J and P as important a part of your personality as the other letters or are they there just to put the fuctions in order.