Largest linear size vs. luminosity of TNG-Cluster radio relics. The color encodes M_500c of the host cluster. The largest separation is measured between the cells with P_radio > 10²⁶ erg Hz⁻¹ to avoid overestimation of radio relic sizes due to the overlapping with accretion shockwaves. Solid lines mark the radio luminosity of the relic with the average surface brightness 1, 0.1, and 0.01 μJy^″−2, assuming the relic redshift z = 0.2 and width 0.2 Mpc. The dotted line marks the lower limit of the available size of the simulated radio relic. The majority of the simulated radio relics larger than > 2 Mpc are identified in massive merging clusters with M_500c > 10¹⁵ M_⊙.