I would second what Greg said about your head. One thing it might be is the mirror. Your set in the video with the pull(looking away from the mirror) looks better than the others but still quite there yet.
Get comfortable sitting in the bottom. Warm up with some lighter ohs and sit in the hole for about 4-5 seconds for about 4-5 reps. Really sit down and feel the position, don't be in a rush.