It is shown theoretically that in lasers with box modes and polarization determined by facet reflectivity, the axis of polarization rotates with viewing direction. For thin double-heterojunction (DHJ) cavities, the angle ρ between the junction plane and the field of the radiation depends on the angles θ and φ in the junction plane and transverse to it, in degrees. It is suggested that this behavior is a useful test for control of polarization by facet reflection. Measurements show the relation is followed in wide sawed lasers with good box modes prepared from a thin DHJ wafer and in a narrow stripe laser from the same wafer. A second narrow stripe laser from the wafer and a single-heterojunction (SHJ) cavity have no such dependence. Qualitative discussion of the measurements reveals information about polarization and mode properties not previously available.