Left panel: Median WARM–to–ICM surface brightness ratio in the 0.2–0.4 keV band for the three cluster mass bins and the ROSAT results of Bonamente et al. (2002) for a sample of 38 clusters. Right panel: Median WARM–to–ICM surface brightness ratio in the 0.2–1 keV band for clusters in the M₄ mass bins and the observational results of the soft-X-ray excess from the Coma cluster (Bonamente et al. 2022). For each line, the shaded area represents the 20th to 80th percentiles of the soft excess within each cluster sample.