SJSinNYC —
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.