Look at what happens when you start the descent. You do a little butt flick, throwing your hips back and causing you to lean forward - THEN you break at the knees. This is wrong, stop doing the butt flick - break at the knees and the hips at the same time. You will probably need to think "BREAK AT THE KNEES" first to get out of the habit of doing the butt flick.
Also, your stance may be a little too wide, and may actually be making it harder for you to hit depth because it is stretching your adductors beyond their elastic capacity. Bring your heels in to shoulder width, then shove your knees out and see if it's any easier to hit depth.