Paying attention to the thumb!

Thumb placement I truly believe depends on the individual. Especially because of anatomical reasons. For example, it is very difficult for me to do things like Joe Walsh because he has larger hands and so hooking my thumb over the neck the way he does is a physical impossibility on some things. I too have looked at where Syn places his fingers and it changes a lot. It depends on what you are getting ready to do on the guitar. For example, 3 Notes per string modal scale runs from the 3rd fret to the 7th fret there is no physical possible way anybody can keep their thumb hooked over the neck no matter how big your hands are. However there are some times when I go to do open chord work that keeping the thumb over the neck helps to mute the top string. So I think it really just depends on what you are trying to play and how big your hands are if you can really physically do it. I sometimes have to pivot my hand a little bit to make things work with my thumb but I have small hands