Ratio between the signal and the total uncertainty for B-mode power spectra derived with the different power spectrum estimation choices. The results are quoted relative to the highest ratio obtained for the biased map. The loss of precision of the spectra derived from the unbiased map is apparent and related to the strong correlated noise modes present in the map. The loss can be mostly recovered with help of a progressively more aggressive removal of the noisiest modes as expressed by the increasing value of parameter α as defined in the text and given in the legend.