look at the movement, the lats extend the humerus and adduction, they have a very small role in thoracic extension. He is arching his back at the end of the movement making the ROM shorter and thus activating other muscles. He is bringing the weight to his hip making the rom shoter again as he is not horizontal, more like 60degrees. Let the dumbell drift forward on the eccentric portion to increase the flexion/stretch on the lats, and bring it up in a slight arc to mid back, thoracic level with no back arching.
It's just simple biomechanics, some people say this works best for me etc, but we are 99% the same, and there are to many extraneous variables to make that comment like people do. Muscle responds best to slower eccentrics and explosive concentrics through full ROM.
