I've been thinking and pondering all of this for the past few weeks. I've dug up some interesting info, and come to come conclusions.
Nardi doesn't know me, and has never met me. He also admitted that while ENFP was his best guess based on the static data that INFJ is a close second, and the two types have similar static maps. He said my pattern was "definitely NF, leaning introverted, possibly more NFP than J" and he said he was fairly certain that if we hooked me up to the machine that an ENFP pattern would be clear. He also said that my pattern is pretty clearly N dom. However, all of that is assumption on his part. I give his assumptions a lot of expert weight, but in the end its still assumption.
However, I know Ne doms. I'm fairly certain I'm not one. They're fairly certain I'm not one.
My chiropractor knows me, and has for years. He insists I have 8 energy, just the "in your face" version of 8. I know 8's. Aside from my conscience (NF) being stronger than theirs, I keep pace with them, and generally like them when they're not locking horns with me. Even then, if they can back down and still be cool, I respect them afterwards.
Therefore, if I am an ENFP 8, I would be a very clear ENFP and a very clear 8, as those two types mesh well together... Ne being outward focused and Fi being self focused. My Ne and Fi would be "all up in your face 24/7". There wouldn't be any ambiguity about my Introvert/Extrovert axis. That's simply not the case.
When you add 8 to any type, you get a boost of E (8 is outward focused) and T (8 falls back on 5 to support it), and to some degree a reduction in J (because 8 is reactive). Add that to ENFP, and you have an extremely E, strong Te, and solid P. Add that to INFJ, and you have an ambiguous I and J, with a strong Ti. Who does that sound like? This guy.
When I get unhealthy (confused, overwhelmed, don't feel like I'm in control or have mastery enough to be confident, etc.), I go to 5 and spill mental energy and seek advice (like now) and am prone to Ni-Ti loops. When I am at my best (or simply leaning toward healthy), I am more like a 2, and my Fe shines through. When I'm at normal mode, my Se and Fe are pretty strong for an INFJ, but they're 8 driven making them seem kinda like ENFJ, but not really.
However, there is no such thing as type. There are only factors that create a whole which can be defined as type. My factors have a lot in common with several types, but, it seems clear to me that they also combine to create something atypical to all of them, which has caused the confusion. I'm not the only one who has developed atypical factors. If I was, Socionics wouldn't have come up with subtypes to try to explain the people who don't fit the standard models. Ni-ENFj is perhaps the best description I've read that could pertain to me, but this subtype could be the result of several combinations of factors... INFJ with an extroverted leaning Enneatype like 8 or 7, ENFJ with an introverted and NT leaning Enneatype like 5, etc.
Okay, I babled on long enough. If you bothered to read this, I'm sure you get my point. So, here's some info I found on INFJ + 8 to keep the thread having more value than just me wrestling with my factors and type.
When they are working together, INFJ and 8 are an amazing balance of masculine and feminine. 8 brings assertiveness and confidence while INFJ brings insight and compassion. At the healthiest stages, it looks a lot like 2, but without the manipulation or neediness, and certainly none of the vanity. (It is flat out overconfidence, regardless of how anyone else feels about it.) All of that 8 inner strength is focused on helping others and making the world a better place while the INFJ talents lie in seeing what needs to be done and envisioning a truth beyond what simply is.
At the average to less healthy stages, 8 begins to lose its compassion and push for what it wants, which begins to turn Fe into a demanding sense of how things should be - rather than being supportive, protective, and magnanimous. The INFJ insight becomes a radar for manifesting those drives into reality. We become even more pushy, insistent, and willful, but begin to hold our own desires in equal weight to the needs of others - sometimes crossing the line of putting ourselves before others. This is an issue, because as 8's, we are much stronger than most people, but can't see that while we're engaging our will. This can lead to inadvertently hurt feelings, which makes our INFJ side feel very guilty.
At unhealthy stages, we lose our empathy, and know exactly how to achieve what it is that we want... with unyielding drive. Anger and lust issues are very common at this stage, and though INFJ 8's usually do a good job of keeping them under control due to the subconscious influence of knowing the consequences of our actions, when 8 gets unhealthy enough, we temporarily lose our ability to care. Any inadvertent hurt feelings we cause here are obviously the fault of their weakness, not our strength, and therefore they deserved to be hurt. Follow my lead, or get out of the way.
At extremely unhealthy stages, we turn into predators fueled by our instinctive lusts (anger, sex, hunger, pleasure, etc.) that have the cunning of our nearly psychic insights. Everyone and everything are prey to devour or resources to exploit... or simply sport for us to unleash the built up rage we so desperately try to keep locked within us.
Needless to say, we generally feel very bad about these sorts of behaviors once we start to get back to feeling healthy. I really don't like to apologize, so it's a double whammy. Apologizing says "I was (am) wrong and I was (am) weak" while at the same time while being an act of weakness (supplication) in and of itself. Therefore, INFJ 8's spend a lot of time in internal conflict once they begin to see the pattern that their core motivations tend to create.
I do need to point out that most INFJ 8's seem to be more concerned with asserting themselves in their "fantasy lives" (idealism and imagination, spirituality or philosophy) than reality, and often have a drive to make their idealism a reality somehow. A key motivation for healthy INFJ 8 is to make the world as their Ni+Fe know it should be by reacting to the world as it presents injustices to fix. The other key motivation for INFJ 8 is to keep the beast that is within us from getting out.
Eventually, we learn to merge the two, but they are oil and water - which means it requires constant conscious acts of stirring to keep them mixed properly. Otherwise, they will separate, leaving us to operate from two opposed sets of motivations and perspectives. Very strenuous.