Top: secondary-mass distribution of the PCEBs in our sample. Bottom: initial mass-ratio distribution. Apparently, the mass distribution peaks at  ~0.3−0.35 M_⊙, close to the limit for a He-core WD companion with stable mass transfer. The initial mass ratio increases towards low values with a steep decline for very low values. Black is for systems containing He-core WDs, while grey is for the whole sample. (IK Peg was excluded from the top panel owing to its high secondary mass compared to the rest of the sample.)