20% efficiency? Love to hear where you got that number and what that means to you. Are you talking protecting individuals wearing mask or reducing the spread overall.Masks have 20% efficiency at best.
If you are talking protection from an individual wearing a mask I’ll go with 20-60% protection as well but that is not what I’m talking about. It about the synergistic result at reducing spread. Anti maskers just don’t get it for some reason. You protect me by wearing a mask more than I protect myself by wearing a mask especially cloth masks not always on right.