I have heard so many things about where your thumb is supposed to be placed when you play, but all of these seem really awkward for me. They say that you are supposed to imagine a halfway line running along the back of the neck and never put your thumb higher than that. With my abnormally large thumb, this is very uncomfortable. I understand that new things may feel weird at first, but doing this makes me end up with a really flat, sloppy hand. And when i get down to the lower frets, my thumb wants to just wrap all the way around the neck. Any advice?