This is a question about skirt lengths. From this answer:
The halacha is that "tefach b'isha ervah" - a tefach (about 3.5 inches) uncovered on certain parts of a woman's body is ervah - nakedness. (B'rachos (24a) in the name of Rabbi Yitzchak). The arm must be covered at least to the elbow and the leg must be covered at least to the knee.
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Rabbi Getsel Ellinson (Woman and the Mitzvot: Volume 2) - Pg. 186, note 37, writes that it is probably okay to pray as long as there's less than a tefach uncovered above the elbows and knee. However, it is certainly absolutely forbidden to pray in the presence of a woman whose skirt does not cover past the knees when she is sitting down, because the skirt will not cover ervah.
My question is as follows: if opaque stockings (tights) are worn under a skirt, may the skirt then be any length? Would a skirt that hits more than a tefach above the knee be acceptable in this case (presuming that the skirt falls within the bounds of aidelkeit and concern for the local standards)?