I have been playing guitar with my thumb placed behind the neck of the guitar all the time. I only place my thumb above the guitar when string bending. I’ve noticed plenty of guitar players (including Syn) play with their thumb above the neck of the guitar when playing on the high strings. Is this a bad habit I have developed that I need to undo? Should I be placing my thumb above the neck of guitar when playing on the b or the high e string, or does it not matter?