I wouldn't worry much about a 20.1 for that very reason, the mylar film is in the shade most of the time. The 20.1 is a different animal due to the design of it magnet structure, the magnets on both sides of the driven element act to keep the magnetic flux constant. The even magnetic field strength on both sides of diaphragm lowers the 2nd harmonic distortion produced by the speaker a lot,result, clearer more transparent reproduction of music.
Scotty