Centre: two-dimensional histogram of the orbital period and WD mass distributions in CVs for our reference model. The colour intensity represents the sum of the formation probabilities of all CVs residing in that two-dimensional bin. The vertical dashed lines mark the upper (3.18 h) and lower edge (2.15 h) of the observed period gap (Knigge 2006). The hatched region indicates the parameter space in which mass transfer will become dynamically unstable, assuming q_cr is given as in Eq. (1). The dotted line marks the shape of the dynamically unstable region if one assumes a constant q_cr of 0.695 for M₂ ≲ 0.7 M_⊙. These regions are depicted in the same way as their corresponding regions in Fig. 1. The dashed-dotted line marks the region where mass transfer becomes dynamically unstable if one assumes the ZAMS mass-radius from Tout et al. (1996). Bottom panel: orbital period distribution of the CVs in our reference model. Left panel: WD mass distribution of the CVs in our reference model.