For a simple two-site exchange between Ba-rich and Sn-rich environments, increasing temperature would be expected to produce a broadening of the associated resonances before their coalescence into a single resonance with an intermediate chemical shift. We do not observe such behaviour, and instead the peaks assigned to Ba-rich and Sn-rich fluorine environments remain distinct across the investigated temperature range. This behaviour is consistent with only some fraction of fluoride ions in Ba-rich environments undergoing exchange with ions in Sn-rich sites, with this fraction gradually increasing with temperature, and with this Ba-rich-Sn-rich exchenge process being slower than exchange between different Sn-rich environments ; i.e., on the same timescale of exchange between Ba-rich and Sn-rich environments, fluoride ions in Sn-rich environments undergo exchange between several different Sn-rich environments.