Period distribution of different kinds of post-common-envelope systems. Left: top: all HW Vir systems including the HW Vir candidate systems from this paper (gray); middle: known eclipsing WD+dM/BD systems from Parsons et al. (2015) (blue); bottom: known sdB+WD systems from Kupfer et al. (2015) (white). Right: top: known eclipsing binary central stars of planetary nebula showing a reflection effect (red) and noneclipsing binary central stars of planetary nebula showing a reflection effect (orange³); middle: known sdB + main sequence companions from the Roche lobe overflow channel (Vos et al. 2019, light-gray); bottom: post-AGB binaries from Oomen et al. (2018, dark green).