I'm sorry, but I've never found xNTPs hard to figure out. There's nothing enigmatic about them. Though being stripped of that supposed Sphinx-like aura seems to bother them a great deal. Shouting "You don't know me! I'm a great big mystery!" doesn't make you any less transparent to certain people. Transparency has nothing to do with how complicated you are as a person.
I'm transparent to my ENFP sister. I just deal with it.
INFPs can keep me guessing. I know their moral baseline and who they are as a person, but the reactions can be wide and varied, so I tend to wait on how they react to something to know how to be supportive.