UPPER BACK TIGHTNESS: SQUEEZE the bar with your hands, set up in uprights, set on the shoulders and then SQUEEZE your shoulder blades back and together to really create tightness in the upper back. VISUALISE yourself snapping or bending the bar across your back while squatting and pull down and across, like a behind the neck lat-pulldown. This can help staying upright in the hole
TORSO TIGHTNESS: BREATHE into your belt and VALSALVA all the way down and up.
HEEL DRIVE: When descending and coming out of the hole, FEEL the weight on your heels, like, REALLY try to feel the entire weight of the bar-lifter system on the heels of the feet.
Hope some of those cues help. Stay strong!