Histogram distribution of the α parameter, σ_α error, and χ² obtained by applying the BAO fitting pipeline to each of the FLASK simulations for the ACF estimator using the fiducial configuration. The rows from top to bottom show the results for each redshift range, the lower (1−10 z-bins), the intermediate (11−20 z-bins), and the higher redshifts (21−30 z-bins). The average redshift for each range is presented in the first panel of each row. In all the plots, the solid blue, dashed red, and dotted green lines show the distribution of the parameters resulting from analyzing the 21 cm only simulations (21 cm), the noisy 21 cm simulations (21 cm + WN), and the BINGO-like simulations (adding also the foreground residual; 21 cm + WN + FG), respectively. All these results correspond to the N_s fraction of the mocks. See Table 2.