The entropically favoured orientation at the vapour interface is side-on, in contrast to the alignment at the solid substrate, but again can be rationalised through excluded-volume entropic effects. Importantly, in all cases studied here, the orientation at the vapour interface of a fluid that is isotropic in the bulk is predicted, and generally observed, to be side-on. Conditions for which the face-on orientation is favoured appear to be difficult to achieve for an isotropic bulk liquid phase for interactions typical of OSCs, but can be obtained if the system has a bulk liquid-crystal phase. Tuning of molecular shape and interaction parameters can result in a shift towards a more isotropic interfacial layer.