This is just my opinion, but saying that a certain exercise gives a peak is misleading because the shape, or mass, has nothing to do with the actual movement itself. When a muscle grows, it's just with an exaggerated shape. You're either working the muscle or you're not, and therefore no "shaping" or "mass" exercises. Best thing you can do it make it bigger.
"flys are for shape, bench is for size"
"barbell for size, cable curls for peak"
This is all crap.