knowing how runway models tend to have stern faces
I don't believe this is the models' choice. It's usually direction from the show's director or from the designer. Some shows are all about the smiles. Some shows aren't. It's a decision made and a direction given.
Yup agreed! Hansel's shows tend to be more fun, where models tend to smile and there's some direction where they "take group selfies" at the end. Couture and high concept stuff tend to be more serious though.