Column-normalized 2D histograms showing the relationship between the δ parameter and the parallel electron heat flux q_e∥fit/q₀) obtained from the CS fits, for slow solar wind (left panel) and fast solar wind (right panel). The color scale indicates the logarithm of the normalized bin counts. The dashed black line represents a weighted linear regression in log-log space, fitted using 2D histogram counts as statistical weights. The shaded region denotes the 95% confidence interval of the fit. The equation of the fitted relation is displayed in the top-left corner of each panel.