Your elbows should be comfortably down. Picture the flute as pivoting on the left index finger, so that it acts as a hinge. Any amount of guiding the foot joint away from you will bring the headjoint closer to your chin. Experiment with this.

The main points of support will be the underside of your left hand index finger, the pinky of your right hand (which depresses its key most of the time) and your thumbs.