when it comes to free weights, it is all about the angle your body has compared to gravity. back exercises mainly focus on the movement of the scapula. when you are trying to build the smaller muscles on your back, they are going to be less engaged since the rhomboid and traps are going to overpower them, and if you do not choose a good angle for your body, you are going to include too much momentum that the impact on your delts is going to be minimum.