this chest exercise is kind of a variation of fly, in which the focus is only on contraction rather than the full range of motion. I personally prefer to do this exercise in supersets to fully fatigue my chest without the risk of injury. the more you push the ball, the more contraction you get. try to bend the wrist backward a little bit(wrist extension) and spread the fingers out for better results. also as you can predict, by bringing the arm up or down(shoulder flexion and extension degree), you can target different fibers.