Binned electron fraction (Y_e) versus ejecta velocity (v), plotted for the 3D models shown in Fig. 14. Vertical bars indicate the full range (thin lines) and the interquartile range (thick bars) of Y_e values in each velocity bin, with markers denoting the mean. The bottom ribbons show the kernel density estimate (KDE) of the velocity distribution for each model. The left and right panels show ejecta sampled at early and late periods of evolution, respectively.