Distribution of uncertainties on viewing angle (Δθ_v) as estimated by GWFish vs injected θ_v of our fiducial population of BNS mergers for different detector configurations (ET, ET+CE, and ET+2CE) and for different pre-merger alert times (15 min, 5 min, 1 min) and at the time of the merger. The solid lines correspond to Δθ_v/θ_v = 0.1 and 0.5. The vertical color bar indicates the redshift of each event. The plots show only the BNS mergers below redshift 1.5. The uncertainty on the viewing angle, Δθ_v, is larger in the case of on-axis events.