@ bold: do you have any data to back that up?
And how do you account for induced/learned deviations from whatever one could say the norm to be, e.g. environment, upbringing, education,
et cetera ad infinitum ?
Ah. At last. I was wondering when I'd get some opposition..
The template of signatures was first made from people who are not actors or trained in any form of facial control. Mostly they were extracted from people I/we had firsthand exposure to; people who we know personally and psychically - people whose type we're sure of. These closest to us were observed, then we noted when and why their face manifested certain expressions - depending on what mental process they were engaging at that exact time. When doing memory recall, certain things were noticed, and when articulating, others. When explaining an ethical decision, others still. And the template expanded.
And as we/I have applied that template outside of them to those who have had education in acting/etc I have seen that off-stage even actors default to their natural facial manifestations. There is one function that is most prone to facial control, however: that being Fe. Fe has the ability to manipulate the face to put on a charming or hostile presentation to others. But ironically, in its ability to control the face it also gives itself away. There are also more than just one cue we check for each function, and generally even if one is blurred by culture/environment the others will still come through.
But for the slight possibility of a habit obstructing the read, this danger is dramatically reduced when the interviewee is asked challenging questions. When engaged in a conversation that forces a person to dig deep into their thoughts/memories and articulate all at once, it is near impossible to also keep control over your face. It is like trying to speak two languages at the same time, it doesn't work.
For instance, if you are an Ne+Si user (and those of you who are can try this out) and you try to
not deflect/divert your eyes as you do intense memory recall or brainstorming, you'll find that your ability to think will dramatically lower, if not be entirely unable to think. For Ne/Si, the eyes need to be left loose/free to roam about for the mind to properly cross-contextualize imaginations with information.
For Se+Ni users, the opposite is true. Their eyes need to be steady/focused in order to process. If they're asked a very challenging question, like describing a place in exact detail, while their eyes spastically look everywhere they will have a hard time coming up with an answer. This would be no problem for Ne+Si users.