Upper panel: azimuthal scatter of the y-parameter (solid line) and of the X-ray surface brightness in the 0.3–0.8, 0.5–2 and 2–10 keV bands (dashed, dotted and dot–dashed lines, respectively) as a function of distance from the cluster centre. The values represent the median computed over the whole sample of 62 haloes in 12 azimuthal sectors. Lower panel: as upper panel, but for the 2–10 keV surface brightness only, computed with three different physical implementations: AGN (solid line), CSF (dashed) and NR (dot–dashed). The grey-shaded area encloses the quartiles of the cluster sample for our reference model.