In Rabbi Falk’s sefer, Oz vHadar Levusha, p329-330, he states that “see through tights are unacceptable because when such tights are worn, the legs remain fully visible and even more attractive than legs that are not covered at all.”
Then, in response to how much of the legs need to be covered- “Although the lower sections of the legs must be very well covered.. there is no obligation to screen off the legs so that they cannot be seen – in contrast with the upper section which must be hidden and disguised behind a dress or skirt. The upper sections of the legs contains the thigh, and the thigh and all that belongs to it must be completely screened off. This obligation does not apply to the lower sections of the legs which are not part of the thigh area.”
Brotherofurs, does this answer your question?