Ratios of various line luminosities for the whole grid of magnetar-powered models as a function of time since explosion. We show the ratio of the [Ne II] 12.81 μm luminosity relative to the optical luminosity (top), the ratio of the [O II] λλ7319.5, 7330.2 and [O III] λλ4958.9, 5006.8 luminosities (middle), and the ratio of the [O I] λλ6300.3, 6363.8 and [O III] λλ4958.9, 5006.8 luminosities (bottom). Different symbols are used to indicate the volume filling factor (i.e., clumping) and a color coding indicates the He-star mass. The horizontal black line corresponds to the observed counterparts for SN 2012au at 2269 d (Milisavljevic et al. 2018).