Forecast errors on cosmological parameters for the Gaussian+SSC covariance, using circular masks of different areas for GCph (a), WL (b), and GCph+WL+XC (c). For the three panels, we show the relative difference in % between fsky and psky for each cosmological parameter. The plain lines correspond to the constraints when marginalising on all parameters (cosmological and nuisance) and the dashed lines when there is no marginalisation.