One personal observation based on the P/J crossover thing. I have one parent who is strongly J and one who is strongly P. It was the biggest source of friction between them. I have many things in common with both of them. They divorced after I was married and on my own.
I think that conflict is, to some extent, represented in who I am—a slight P, but bordering on J.
I think it's interesting that can show up in a personality test. But I've taken this thing a bunch of times over the years...and there it is, plain as day.