Kippenhahn diagrams depicting the evolution of radius versus mass (both axes represented in log scale) for low-mass models. The details of the diagrams are similar to Fig. 5. In this version of the diagrams, the change in radius during the pre-MS evolution of all models is clearly visible. All models undergo the luminosity wave at log (M/M_⊙) = 1.3 and experience a strong increase in radius. The next noteworthy evolutionary trend is at log (M/M_⊙) = 1.95 when the models undergo a drop in accretion rate below Ṁ_crit,preMS which results in a decrease in radius. Eventually the accretion rate increases above the Ṁ_crit,preMS.