Number density distribution of visible DWDs as a function of mass ratio and orbital period, where the mass ratio is defined as the ratio of the brighter WD mass to the dimmer WD mass. The red dots are for the observed samples with determined component masses and the green dots are for those with only minimum companion (dimmer) masses determined (Kruckow et al. 2021). Left and right panels are for Ge’s and polytropic models, respectively.