Predicted values of the linear model evaluated at a common reference point (log M_z = 0, [Fe/H]_z = 0) for each progenitor family. Points represent the estimated marginal means, and horizontal bars indicate the 68% confidence intervals derived from the fitted model. After controlling for cluster mass and metallicity, the fraction of first-population stars (f_P1) shows systematic differences between progenitors, with Sequoia clusters exhibiting higher f_P1 values at fixed mass and metallicity.