Spectral correlation ratio versus mean hydrogen column density for the six sky regions. Each panel presents the results for one of the ℓ bins, ℓ = 4–11, 11–50, 50–160, and 160–320. The dark and light grey bars represent the 68% and 95% confidence intervals computed over the 300 E2E simulations, while the blue segments mark the median values. The bottom left panel for the ℓ = 50–160 bin is directly comparable to the corresponding plot from the PL analysis, their Fig. 3.