So when you first meet them, INTJs can look more particular and uptight, whereas INTPs seem more flexible and easy-going; but once you get inside of them and really interact over the long term, you quickly realize that INTPs dig in tremendously when it comes to how ideas are thought about, what can be derived from reality and what cannot, etc. In general, INTPs do not seek to impose themselves on others... but they are "anal" as to what they will accept as valid in their thinking process, and internally they critique anything that goes on outside of them, they just don't often share it. INTJs seem much more flexible internally; it's just their need for external closure that can make them seem demanding at times.
And the same would go for the other IJ/IP pairs (and that might be worth articulating too ) :
It does become confusing if someone has not realized that Socionics is different from MBTI in this regard.One approach is to use a lowercase 4-letter to refer only to strict rationality. Then Fi-dominant and Ti-dominant types will be the lowercase-j's along with the Fe and Te dominant types. But the original meaning of uppercase J and P is not going to go away any time soon, so I really don't think this is the best idea as a general practice.