Orbital period versus mass of the MS component of the WD+MS binary systems. The background KDE contours represent the model (from left to right, A3, B3, C3, D3, and E3). The triangles represent observational data from Table 1. The colors indicate the type of WD companion: teal for He, orange for CO, purple to ONe, and yellow for WDs that can be either He or CO depending on the inclination of the system. Models A3 and D3, both with β = 0.0, are the only models that can reproduce the large-period (P > 100 days), low-mass MS+He WD systems.