I have the doubt either, but I know a little bit of few things
There is the concept of the ambivert, someone who gets bored by being too alone or too much with people.
But that concept is only used to ENTP and ENFP personalities because of the function Ne, the explanation doesnt extend to ENFJ/INFJ.
A lot of people dont accept that there are extroverted and introverted and no middle. I agree that there should be people on the middle, and that there is nothing wrong with that. But there is one thing about MBTI, it is that not all the sites uses the definition of extraversion or intraversion as "party people" VS "home people". Some say its about where you get your energy, if it is from socializing or "homalazing". But there is one key aspect about function stacks (there is one fixed topic here in this sub area about them), and these are supposed to clear it away. Just quoting myself from other thread:
"I would like to frame my point of view on this, so what I am going to say next is more explainable and easier to understand. Some people say that the function stack should be in perfect order, but it never happens. So, thats it is my perspective indeed but it doesnt mean that it is wrong, is that in the function stack, the 1st function is supposed to be in first in the tests, the 2nd function is to be in second place, the 3rd function should be in third place, all that if there is no introversion or extroversion main functions split (Ne=Ni for example is a split), but the 4th function is supposed to be in the 7th or 8th position and all other functions are free to move along the stack, giving the personality uniquiness and very deepness. Because if the 4th function was really in 4th position, the descriptions "lack of the 4th function", which is "lack of Si" for ENFP, wouldnt make any sense at all. The 4th position is in the middle, it is not supposing to be lacking, I never saw any sense on that, but there is a good tone of people who disagrees with me. People say lack of Si, but in that sense they should write about the lack of Se, lack of Ti, and so on, but I never saw anyone describing that. Also, Jung originally, I say I think because I didnt read Jung book about personality yet, doesnt have any specific order for his 8 functions, the order came later in Myers Briggs. Jung originally acceppts almost any function stack order. And one more thing, the complete and perfect function stacking admits and types the subconscious, I dont remember if it is the reverse in the 4 letter code or not (ISTJ for ENFP), but there should be in deep psycology several famous and accepted names on that area (such as Freud) that wouldnt agree at all that the unconscious/subconscious is simply some kind of reverse of the subconscious. Typing is not that easy on the conscious level, in the subconscious is even worse. I dont think that "since your conscious is ENFP so your subconscious has to be ISTJ and cant be different" really follows"
So, for ENFJ, the third function is Se, and the weak one is Ti.
For INFJ, the third function is Ti, and the weak one is Se.
Thinking this way, what differentiaties an introverted ENFJ or a extroverted INFJ are these functions. For as I know of function, through a more superficial way, you could try reading websites about thertiary Ti (in INFJ) and then read about thertiary Se (in ENFJ) and see which you think is the best. Or take a cognitive function test and see if you can see clearly and consistently if your Ti is higher than your Se or the oppositte (or if they are equal, which would make you go back to square one).
First description would be a person that is more dreamer than usually, that usually dont pay attention at stuff around (usually forget keys, usually say 'ops', etc...). This people is able to have thoughts relatively organized, capable of being more conceptual and has kind of a philosophy vie. It is likely, although not all the cases, that this case has a F/T reasonably close to each other.
Second description would be a person that, although it has its own visions and intuition, it is more grounded, likes to enjoy experiences and the present moment, although it is less argumentative, and it is indeed really a feeler.
The first description has Ti in the 3rd stack and Se as weakness, and it is relative to INFJ. The second has Se as 3rd place, and Ti as weakness (achiles heel) and describers ENFJ.
Hope it helps, although I dont think that it really solves your issue. You could try that or accept that you are an ambivert (although you wouldnt be able to "blame" Ne or Si for that), but maybe someone can clarify better than me.
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