Let me try this again. I'm including a pic of Thomas Stevens that shows he's fairly flat where it counts--on the lip tissue. I also included a pic of my chops before playing. This is will serve as a standard for a teardrop lip that is allegedly problematic.
My theory is that if you have a fairly sharp teardrop, the problem is not that it diverts the airflow, the problem is that it creates so much loose tissue that it limits the vibration according to it's size--as in length and thickness of strings or reeds, etc. The sharpness of the teardrop essentially limits the frequency and thus the range of the player. Since lip tissue is highly elastic you can easily squash any teardrop lip to create an airtight seal with your lower lip. You can then create an aperture in the center of your lips, however, because of the extra tissue, you are forced to create a larger aperture than you would if your upper lip were flat because the compressed tissue of the teardrop expands. You might think you could simply play with the tissue compressed. Well, experienced players know that you cannot play high notes well if you "pinch". That is, the notes won't sound well if the vibrating surface is compressed. Therefore you are forced to create a larger aperture with a sharp teardrop to relieve the pressure and that larger aperture means more lip material is vibrating and thus you have a lower note. The teardrop essentially limits your effective range.
Thomas Stevens E | Flickr - Photo Sharing!
Ra Straight on | Flickr - Photo Sharing!
A teardrop lip is not an either/or situation. No two lips are identical and perhaps most people have some added tissue in the middle of the upper lip. There are many great players with a bit of a "teardrop". What counts, I believe, is the angle of the slope of the teardrop. The greater the angle the greater the effect on limiting the effective range.