Re chaverim: sorry I wasn’t clear. He made it clear that the whole kneecap should be covered at ALL times, therefore skirts should be longer than the bottom of the knee to enable this.
And for the record, I have no problem with the two shirt look. I think it’s cute. I guess it’s because you can’t wear too full a shirt as the bottom layer but there are somewhat tighter sleeved shirts that aren’t too tight either.