Comparison of data-driven to simulation-based corrections for secondary particles impinging on the FMD. Different markers correspond to different collision systems and energies, and the colours indicate the five FMD rings. $S(\eta)$ is shown for 0cm< IP$z$< 2cm as an example, while $E(\eta)$ is independent of IP$z$ (see also text). Pythia was used for pp collisions, and the Pb-Pb points are from simulation with a parameterisation which include the available ALICE data on particle composition and $\pT$ distributions. Black circles correspond to $E(\eta)$.