Flattening that chin is just a hard concept to understand. Now, try this little pastime. Do this: Place your thumb and index finger on the back of your hand. Press down and pull the palms apart as if you're stretching the surface of the back of your hand from among those two arms. Now, put the clarinet mouthpiece on your mouth, anchor your lower lip with the reed, close the mouth off around the mouthpiece and flatten or point the chin. If you're knocking down accurately, the skin among your lower lip and chin should stretch or “firm up” like the skin on the back of your hand stretched by the arms. Clarinet is held too high. This angle of clarinet affects embouchure poorly. Between a 30 and 40 degree angle is often authorized as correct. You can test this by listening for your sound as you move the clarinet around. Try this: set your embouchure, move the bell of the clarinet too high.