Video 5: Four Points of Contact and a Fifth
Video 6: The Moveable Point of Contact–Using the Left Hand
These two videos contain most of the information that you usually get in a demo of how to hold the guitar for playing classical music. Check and see how and where all the points of contact show up for you in your poise and posture. Pay special attention to the height of the footstool and the height of the chair and how the guitar feels at different heights for you. The size of the guitar makes a difference as well!
I’ve often seen students who grew used to setting the footstool too low. A low footstool can lead to technical difficulties in left hand reach, and you might find that this improves with a higher adjustment. Check and see if there are other ways you’re holding the guitar that are forcing your hands/fingers to overcompensate. These are things you should play with. While it’s good to develop some comfort playing the instrument in various postures in an informal way, if you want to have a dependable technique, I recommend continuing to refine the details of how you sit.