Thanks for pointing out the often overlooked world of ergonomics and posture when playing. It can be hard with video lessons to correct these problems as we simply are not there in front of you to correct your posture or hand position. That is why outside of your GT work you should study privately (if possible) and if not, make sure you play with other musicians that can also provide some additional words of wisdom. Good luck and again, let me know what chord shapes you are trying to play.