Backhand topspin key points

Hi PingSkill Coaches,

I've been comparing the start position and the body movement during the backhand topspins of Persson, Waldner, Samsonov, Kreanga, KongLingui and WangLiqin from training footage. Most seemed to start the bat at knee to mid-thigh height, although WangLiqin and Samsonov often began at shin height off underspin shots. Most started with their bats at around 30 to 45 degree angles from the horizontal, so their bats were very closed. KongLingui and Kreanga often had their bats parallel with the ground and Kreanga sometimes had it angled backwards or at -10 degrees to the horizontal. At contact with the ball most had their bats closed at about 45 to 60 degrees from the horizontal. To achieve this change from 0 degrees, Kreanga and KongLingui rotated their lower arms from the elbow before starting the main part of their stroke. They both kept their wrist bent back fully, ready to release it on striking through the ball for maximum wrist action at contact. Persson was the best at keeping the low sitting position with the upper body hardly moving. Kreanga was also very good at maintaining balance, but initiated his shots with a large shoulder turn, sometimes up to 45 degrees at the waist from the square on position, but kept a very steady head position throughout. Waldner tended to bob up and down, with the angle between his legs and upper torso increasing as he pushed up through the stroke, straitening his body. This upward movement was even more pronounced when he used maximum power, lifting both feet just off the ground. KongLingui was similar to Persson off block shots, maintaining a seated position, as his arm swung forwards, but off push or chop, his bat swung more upwards and so his head tended to lift upwards and backwards as his body straightened towards the vertical. Samsonov was similar to this off chop. WangLiqin had the most upper body movement, with loss of balance and feet movement when playing off chop. His upper body would move from leaning forwards to vertical or even just leaning backwards, with his left foot slipping forwards as he lost good balance.

So what are the key points to concentrate on for intermediate players?
What range of start positions, hand positions and upper body movements are good practice?
Looking forward to seeing all the finer points demonstrated in a video from you!