For peaks you have to flex and squeeze the peak during the contraction, and make the exercise into a posing/flexing exercise. Don't need a ton of weight. The best movements are the ones that put your arms in the pose positions. If using free weights, preacher curls, steep angle drop off, squeeze and flex the peak as hard as you can at the top. The pump should be focused entirely on the peak. But machines work good too, probably even better. Preacher varieties or the kind that get your arms up almost like a double bicep pose but with them in front of you. Another variety is standing between the pulleys and just doing a double bicep pose while holding the handles (moved up to about shoulder height