That's funny - my underneath is more 2b also, but my technique has gotten better at getting that section to curl up more. And surprisingly, the length helps with that section. But my 3a (sometimes even 3b) parts are the front sections around my face, especially above my ears, and the back and canopy is my 2c section. Most of the time I just don't worry about it. If I really want my curls to be more uniform, then I will take some extra time to twirl different sections.