The geometry used in determining the normalisation for the APEC modelling of the radio relic regions (Eq. (5)). R_cc corresponds to the distance between the relic and the cluster center as projected on the sky. R_l is the relic largest linear size and R_w is the relic width. For relics that are classified as roundish by Feretti et al. (2012) we use R_w = R_l. φ is given by . In result, the dashed curve is the solid angle over which we integrate. The relic image, corresponding to the so-called Sausage, is adapted from Röttgering et al. (2013).