Yeah, that's it. If you want to raise it, just make sure that the smallest slices are selected when the character looks angriest or frowns. That will give the smallest decrease in the number. The slices are proportional to how they affect the person. Bigger slice=bigger change. When they look happy/smile, it goes up. When they look sad/angry, it goes down.

But what makes them happy/sad changes from person to person, so cycle through the selections to see how their face changes first.