Top: Map of EM computed from the electron density derived with Metis, as is described in the text. Bottom: Comparison between the count rates measured in the FSI 17.4 nm passband (horizontal grey bands) and the expected count rates (red bands) calculated from the EM according to Eq. (4), in the eastern (left panel) and western (right panel) streamers (the values are shown with the corresponding uncertainties, as is explained in the text).