Variations of simulated light curves with a varying impurity parameter, Q_imp, in the accreted crust (left panel) or varying shallow heat, E_sh (right panel). In both panels, errorbars reproduce the observations at the cooling stage after outburst I and the solid red curve is the best-fitting curve 5 from the left panel of Fig. 17. Other curves show the light curves with increased or decreased Q_imp or E_sh, according to the legend.