1. If they are asking about tznius, then they care and “barely covering the knees” will not be enough.
2. You didn’t state at the beginning (I didn’t read every post) but I tell people before they can even ask one question:
a) “I only answer questions from the parents of the boy/girl) Playing telephone with peoples lives is never a good idea.”
b) I don’t answer any physical-looks questions.
3. I never answer an open ended question. I channel my inner “Colombo” and just look at them blankly and reply “I don’t understand. Can you clarify what you mean?”