Dependency of the level of systematics on the parameters α, β, and η of the PSF error model. Upper panel: Dependency on η with α and β fixed. It follows the dotted line in the left panel. Middle upper panel: Dependency on α with β and η fixed. It follows the dash dotted line in the left panel. Middle lower panel: Dependency following the degeneracy (solid line in the left panel) in the (α, η) plane with β fixed. Lower panel: Dependency on β with α and η fixed.