Evolution of the asymptotic period spacing for overmixing models with α_ov = 0.1 (blue) and α_ov = 0.9 (pink), computed with the default core boundary scheme (dark colors) and the CPM scheme (light colors; see text for details). The arrows indicate the moment in the evolution at which a semiconvective region appears. Strong episodes of CBP are visible in the low-overshoot models for Y_c < 0.15.