The chest consists of pectoralis major and pectoralis minor . Pectoralis major consists of two heads clavicular head is the top part and is more commonly called upper chest.
Sternal head is the rest of the chest including middle and bottom of the muscle.
It works your entire sternal head which is most of your chest. Lowering the bar to two inches above your chest is also acceptable, that will keep constant tension in your muscles. With dumbbells you have the advantage of lowering the weight on the sides of your body below the level of your chest and that will stretch and stress your chest a little more. Amount of weight and lack of balance are some of the culprits that will prevent you from getting the most out of this exercise. Perform it the same way as flat bench press the only difference being the incline.