Where does the 4″ rule come from? I think its a chidush of R’ Falks.
From looking at pictures of 30-50 years ago, the skirts were alot shorter on the Rebbitzens than they are today. Take a look at your parents or grandparents wedding pictures. The skirts are not exactly what we would consider Bais Yaakov length of todays generation. When we were growing up, knee leangth was for the frummies, but the 4″ rule signed by some anonymous vaad means zilch!