BlackCat - you might be the perfect person to help with this, because Type 8 is one of the types in question. First time I took the test, I scored as an 8. I read the description and discarded it pretty quickly. For one thing, I'm female, and didn't really want to identify with such a "masculine" type. For another, type 8 descriptions are so clear cut - almost any deviation calls the type into question. For a little while I thought I might be a 1, but I have a tendency to cut corners, so I tossed that out pretty quickly.
I finally decided I was a 6, and in many ways, that's a very good fit. It's pretty easy to write-off 8-ish behavior as a CP 6. But no matter how hard I look, I just don't see my 8-ish side being counterphobic: 8 feels like the "healthy" side and not a reaction to anything. When I'm comfortable, I get more controlling, take on more of a Leader role, express opinions more freely, take charge of situations, argue for fun, find things to compete over... it seriously isn't a response to fear - it's me at my happiest and it all comes very naturally. Since I was a child, I've been told that I always had to have things my way. I rarely show weakness and have a hard time expressing softer emotions. Also, I'm rarely ever confused about what I think or how I feel.
But 6 still fits too. I don't like approaching people, and use humor and banter (rather than blunt directives) to connect. When I'm in a new or unfamiliar situation, I have a lot of the self-doubt of a 6 and I try to build alliances rather than simply impose my will. I genuinely want to be liked, which isn't really a concern for many 8s. My mental energy is high, and I enjoy verbal sparring and playing around with ideas (seems like a Head Triad thing). Also, I don't really over-identify with lust - I'm actually pretty good at controlling my appetites most of the time. I value stability over adventure, and despite the fact that I'm very talkative, I'm also quite introverted.
One more important distinction: it really is a matter of the people I'm around and not the stress involved in a situation. I'm pretty 8ish in any situation with people who know me well - whether the situation is stressful or not; similarly, I'm pretty 6ish in any situation with people I don't know as well, regardless of the stress level of the situation. I can even see it with a lot of my posts on this forum. My first few posts were very deferential - toe in the water type posts, and some of my more recent posts have a slight confrontational edge to them.
So, if you eliminate the CP 6 argument (which to me is just an easy excuse for any legitimate 6 vs. 8 confusion), is it more likely to be a 6 who becomes an 8 as familiarity increases, or an 8 who becomes a 6 in less familiar surroundings?