They focus on the peak, but my peak's ok now, so I just superset them right after hammer curls, obviously, with a rather low weight. I think I'm working the entirety of the biceps like this.
Also, quit doing barbell, for 2 weeks or so; start with heavy hammers, then do preachers, then concentrated. If you're strong enough, you could start it all with chin ups, and do back too. That's the way I do it for now, since I'm working everything twice a week.