Curl from a stretch for a wicked peak.
Let the arms hang fully back to load the long head, keep your upper arms fixed.
Lying back on an incline with your arms hanging behind your body puts the long head of the biceps into its deepest stretch, and curling from that position loads the muscle where it is longest and weakest. That stretched-position work is exactly what standing curls miss, since they let the bottom of the rep go slack. It earns its spot when you want to attack the biceps from the opposite end to preacher work.
Somewhere around 45 to 60 degrees suits most people. The lower the bench, the further your arms hang behind you and the deeper the stretch, so start higher and work down as your shoulders allow.
Because the biceps are loaded in their most lengthened position, where they are weakest. Expect to use noticeably lighter dumbbells and treat that as normal, not a problem.
Preacher curls fix your arm in front of your torso, this takes the arm behind it, stretching the long head far more. Both kill swinging, they just load the muscle from opposite positions.
