Interjection
Read this. I don’t think he is stating his “opinion” but rather normative halacha. Find me authoritative sources that disagree.
The Tefach Measurement:
Are there any allowances to keep any of the aforementioned parts uncovered?
Many people who have heard the term, Tefach b’isha ervah, have mistakenly concluded from it that it is permissible to leave less than a tefach (a measurement of 4″ x 4″-10cm x 10cm) of a forbidden area uncovered. This is a serious mistake since the halacha (law) requires complete covering of forbidden areas. The tefach measurement was given only in connection with the husband and very close family saying a bracha (blessing) when his wife is not fully covered, but there is no heter (allowance by law) whatsoever to leave a small amount uncovered in the presence of a stranger, and there is no difference between a tefach and less than a tefach.
Modesty- An Adornment for Life, Rabbi Pesach Eliyahu Falk (pages: 268, 293)