Even according to the Poskim who are matir it, my understanding is that they are addressing a bedieved situation — i.e. if a man is in the presence of a woman with this amount of hear showing, can he make a bracha. They are not stating that it is fine for a woman to intentionally show her hair. Also it is generally explained as this is an amount that often will slip out (as mentioned by previous poster, over the ears or if the tichel slips a bit), and is cumulative. Sheitels/ falls that are designed to “blend” with your hair to create a more natural hairline are certainly not in the spirit of this psak, and in my experience unfortunately don’t even meet the letter of the psak (i.e. much more than “one finger” worth is being shown). It is a similar issue for women who really on this to pull back their snood or tichel and show a sliver of hair: if you start out according to exactly the limits, what happens if your tichel slips back, or hair escapes over the ears — you have lost your “safety zone” and are violating halacha.
Let us get to the heart of the matter (once again).
There are two completely disconnected issues with tznius. The first and the one brought in Halacha (regarding Brachos and the sort) is Erva. It seems to be the consensus that at least some hair (whatever shiur you might want to have, even if it is lip hair) is not Erva.
Then we get into Tznius – the “non halachic/brachos” version (not to say it is not halacha, but the practial application for a male doesn’t really exist for himself), which is dressing in an enticing manner which will attract attention (which is against “halacha” (what I’m not getting into here) for women). This “shiur” is extremely subjective, with Poskim going from one extreme (such as R. Falk) to the other, as per “what will attract attention”. Ask your local Rov what in your area will “attract attention”.
For example, if a woman is completely covered in red (which is not allowed in halacha, due to it being the color of Zonos (Rema YD 178:1), it would not prevent a man from making a brocha, since it is not Erva (as long as he is not distracted, of course).
We have discussed this before, this is just a reminder for some and something new for others.