Schematic view of the cell energy repartition of two high-energy decay photons from a neutral meson, each centred in the black-filled cells,on top of a high-multiplicity low-energy particle underlying event environment, the lightest blue cells. The pink lines are the contour of cells selected restricting the growth of the cluster (V2) used here to calculate the cluster energy and position. The orange square isthe $5\times 5$ region around the highest-energy cell used for the shower shape calculation, excluding cells that only have a common corner, red crossed. The red dotted lines are the contour of a cluster without growth restriction (V1), as used in previous \pp and \pPb isolated photon analyses .