So, part of the combination here is  your arm resting on and kind of shoving the guitar a little bit that way,  kind of pulling it into your body a little bit, the fact that the shape of the guitar has this little area for your leg to go in, it helps keep it really steady  and it should be, not rock hard in this position but solid, because you don't want the neck wobbling around while you're trying to change chords. 