Relative difference, δ_min, between the estimated top hat and the input as a function of the number of COSEBIs filters, n_max, utilized for a few ℓ-ranges. In all cases the saturation level is reached before n_max = 80. The minimum value of δ_min is shown in Table5. In general, a higher number of modes is needed for a narrower top-hat filter, which is due to the spillage beyond the observed angular range (see Eq.(41)).