An outer grip, as you’d use on wide-grip curls or wide preacher curls, works more of the inner head for biceps thickness. A shoulder-width grip works both heads more evenly but may favor one or the other, depending on your individual attachments and neuromuscular efficiency.
So to emphasize your peaks, you may want to try training concentration curls first. That will affect the outer heads. Following Positions-of-Flexion exercise selection, you would follow with a midrange move, like shoulder-width-grip barbell curls, for “even” emphasis.
Train the stretch position last with incline curls, which are more of an “out” exercise. So you have concentration curls, barbell or dumbbell curls and incline curls.
Another “peak” consideration: Do a hammer curl movement to train the brachialis, the muscle that snakes under the biceps. Building that down-under muscle pushes up the biceps for more peak. (Do keep in mind that genetics has a lot to do with how much peak you can acquire.)