\ Ratio of isolated-photon \ptg-differential cross sections measured with $R=0.4$ over $R=0.2$, $f_{R(\frac{0.4}{0.2})}$, for \PbPb collisions at \snnfive and for the 50--90\% centrality class. Error bars and boxes are the statistical and systematic uncertainties, respectively. The pink band corresponds to pQCD calculations with JETPHOX, the width represents the PDF uncertainty, and the blue vertical bars indicate the statistical uncertainty of the calculations.