Yeah, I s'pose I better throw in my two pence since I said it would've been an interesting thread.
I know what you mean, and I don't think it's only these types that are difficult to differentiate between. I for one (I set up a thread on this a short while ago) have trouble telling the difference between an EIE and an SLE (just by observation, obviously). While I'm not so sure Beta Introverts are hard to tell between, or duals, I find SLE-EIE and the two you mentioned are the ones I'm most concerned with.
I basically use the temperaments to decide between mirrors. I sometimes think I'm LSI, but then I realise not only that I prefer IEIs as much as I fucking love EIEs, but also that there are elements about the SLE that just don't fit with the LSI. Besides the IJ thing, SLEs also have more of an irrational (in the true meaning of the word), impulsive air about them. While they may not, in comparison with some of the rest of the socion, look/seem or even be particularly impulsive or irrational, they are certainly more so than LSIs. LSIs are far more methodical, systematic and careful in both thought and deed. They are more difficult to change - while all Beta STs are stable, grounded and confident, LSIs go that little bit more. An LSI is like an oak - totally fucking solid and unmoveable, an SLE like a willow (especially like the one from Harry Potter) - still grounded, but somewhat aggressive when it comes down to it. With an SLE, you'll generally sense more of a kind "FUCKING YEAH MAN WAHEYYYYYYYYYYY!!!!!!!" quality to many of them (especially Se subtypes). With LSIs, there is none of this. Compare someone like Joe Pesci in Casino or Goodfellas (or if you haven't seen those films, any of his films, really) - SLE, probably Se subtype - with Denzel Washington in American Gangster - LSI, probably Se subtype as well.
Hope that helps. I don't feel I know enough about EIEs and IEIs to give any decent distinctions between them.
+1
No it didn't.