To probe the degree to which the local tin environment directs the orientational bias for individual tin lone pairs, we calculated, for each lone pair, the proportion of time that this lone pair points towards each face of the enclosing cubic site. Each Sn has 12 cation nearest-neighbours arranged in a cuboctahedron. For a given ⟨001⟩ vector from the central Sn, four of these cations are infront of the central Sn, and coordinate the fluoride sites on the front-face of the Sn 4a site, and four of these cations are behind the central Sn, and coordinate the fluoride sites on the back-face of the Sn 4a site-the other four neighbouring cations occupy the same {001} plane as the central Sn. Because the local fluorine environment depends on the arrangement of the nearby Sn and Ba cations (as shown above; Fig. ), we consider the numbers of Ba and Sn cations coordinating the front-face and back-face of each tin as an effective descriptor for the degree to which a particular tin has a symmetric or asymmetric local coordination environment.