Cumulative integral of the first and second term of the SOLA objective function, Eq. (C.3), for optimal values of Δ as a function of fractional radius, shown with a blue and orange line, respectively. Panel a) corresponds to the model discussed in Sect. 3, panel b) corresponds to a model around 15 L_⊙, and panel c) corresponds to a model at about 20 L_⊙, that is, right at the maximum of systematic errors in Fig. 6.