I'd say it can go either way between INFJ/INFP for you. I think your need for validation has a bit more to do with your enneagram 4 than MBTI though it's a bit tricky to tell MBTI because both types can be enneagram 4 fairly often. Whether INFJ or INFP, I think you have stronger Fi than the average INFJ though maybe you also have stronger Fe than most INFPs, which leads to quite the conundrum. I agree that after the first time I took the test, it was easy to catch onto patterns in what the questions were asking for, so I felt like any subsequent tests were biased almost by what I wanted to see myself as at the time. I have even manipulated the test once to intentionally try to score as a type I know that I am not just to see if I could (and I succeeded). I think the functional stack is a rough ranking of cognitive functions that actually varies more individually, too. Like, who's to say that an INFJ can't also have strong Ne and Fi? In the case of my INFJ friends, her Se seems like her weakest function rather than fourth place on her stack as MBTI would dictate because she has terrible spatial awareness. My worst function is probably Si because my terrible memory for details hence why history was always my most difficult subject in school, yet my INFJ friend actually enjoyed history partially because she likely has at least comparitively stronger Si than me.
The other confounding factor is that MBTI type is just a starting type for personal growth. As you develop, you tend to become more rounded and develop some of your weaker functions. Of my lower functions, my tertiary Ti has probably improved the most over time to the point that tests sometimes place me as INTJ simply because I value objectivity and logic. I might be a little odd though because I am good with science/math, which they tend to attribute to INTJs stereotypically while many INFJ descriptions recommend INFJs become writers/counselors for the most part. The point is that people are complex and type descriptions are often limiting if you marry yourself to them. Those are my thoughts. Take from it what you will. :-)