its not just genetics.
peak can be developed by doing curls with the elbow in a higher position, like doing headcrusher curls on a cable crossover, bringing the high pulley towards your ear...or by laying down on a bench, curling toward the bridge of your nose from the high pulley.
this type of curl also prevents cheating like you can with standing upright and curling. especially laying down and curling from the high pulley, constant tension and a burn like you wont ever feel with standard curls.