Regarding Rav Moshe Feinstein zt"l who allows showing “2 fingers-worth” (4 cm.) of hair to show -: doesn’t this make the woman "not repulsive" - not just to her husband but to others as well?! Is this permitted to everywhere, even if there are other males around? Won’t this awaken their "yetser" by mistake?

The goal of the hair-covering for married women is certainly not to make them “repulsive” to other men! The Jewish woman should be attractive to her husband, but not attracting, and not distracting, for other men, but not repulsive! Every person is created “in the image of G-d”, and should respect themselves accordingly, and surely should not present themselves nor be seen by others, chalila, as “repulsive”! Our sages halachically define the ideal of modesty regarding a married woman’s hair, that as long as it’s clearly covered, she can leave out this minimal “2 fingers-worth” across her face (4 cm.), and it’s natural and accepted to do so. Accordingly, it’s not considered inappropriate even outside around other men, for a normal man’s “yetzer” should not be aroused by it. It’s worthy to note that the Maharam Alasker (cited there by R. Moshe) mentions that this legitimate custom of women purposely leaving out that minimal amount of hair was done davka in order to be attractive to their husbands.