The high bar back squat is noted for knee flexion, lesser hip flexion, an upright torso and a deeper squat than other variations.

Bar placement:

The hands are as close to the shoulder as possible.  The index, middle, ring and little fingers are firmly grasping the bar.  If using a thumbless grip the thumbs should be as close to the top of or over the bar.  When gripping securely, it is normal for the wrist to extend slightly so the bar is on the base of the palm with the forearms assisting in supporting the load.  The majority of the loaded bar is on the superior portion of the spine of the scapula above posterior delt against the trapezius.  The scapulae are retracted to assist in making a shelf for the bar.

High Bar Back Squat Bar Position on the Pendulum Rack System