Linear regressions for determining the homology relations of Eqs. 3 and 19 and the structure term S(α, β) as defined in Eq. 13 and 20. We use the grid evolutionary track of A19 taken from the STAREVOL (SE) code. Each dot represents one of these stellar tracks, from which different values have been deduced as mean value during their MS (subscript SE). The first row shows L_*, the second row shows R_*, and the third row shows S(α, β). The first column illustrates these different values as a function of M_*, and the second column shows them as a function of ([Fe/H] + 2). The third column illustrates the quality of the fits. It represents the different original values (L_*, R_*, and S(α, β)) as functions of the values that were estimated by the fits (subscript fit). These regressions are illustrated in the first and second columns. They are shown in purple if they are multiparametric (as a function of M_* and [Fe/H]) and in cyan when they are only a regression on M_*. Blue dots represent models on which we perform the multiparametric regression, and the orange group represents models on which we only fit on M_*. For the latter, we divided the values by 10 for illustration purposes.