Inclusive-cluster $\sigma^{2}_{\rm \text{long, 5}\times\text{5}}$ distribution as a function of $p_{T}$ in data for pp (bottom left frame) and Pb$-$Pb collisions for two different centrality classes 0$-$10% central (top left frame) and 30$-$50% semi-central (top right frame). The dotted line corresponds to the tight value of the upper selection limit for single photon candidate clusters (narrow clusters) and the dashed line corresponds to a looser photon upper selection used in Pb$-$Pb collisions below 18 GeV/$c$. The dotted-dashed line corresponds to the narrow cluster's lower limit.