Average relic surface brightness vs. redshift. The colour of the points shows the relic LLS. Triangles denote candidate relics and plusses those relics which are part of a double relic pair. All other relics are plotted as circles. Red circles surround relics in clusters which also host a RH. PSZ2 G069.39+68.05 and PSZ2 G107.10+65.32 are labelled, with the labels below and right of the data points. The dotted black line is at 2σ_50 kpc, where σ_50 kpc = 0.216 mJy beam⁻¹ is the average rms noise of the 50 kpc-tapered images in our sample.