Cation-vacancy sheelite-type phases in the Ca1-3xBi2x[]xMoO4 system (where [] represents a cation vacancy) are being investigated for applications in wireless communication because of their microwave dielectric properties. Using X-ray powder diffraction we have found some subtle structural variation with increasing x-value leading to the eventual appearance of superlattice ordering at compositions above x = 0.15. Three compositional ranges have been identified and this proposal seeks to characterize the nature of the superlattice ordering and whether this ordering appears at the local level at lower compositions and can explain the non-linear chemical expansion seen between x = 0.075 and x =0.10. Both the long-range and short-range structures will be probed using reverse Monte Carlo Modelling of total X-ray and neutron scattering data.