S/N threshold determination analysis. Top panel: Cumulative S/N distributions of positive (E_S/N) and absolute negative peaks (${\hat{E}}_{S/N}$) in the E-mode map detected with SExtractor. Bottom panel: Difference in cumulative counts of positive and negative peaks as a function of the S/N. The S/N threshold achieving a 70% purity is defined where the cumulative positive peak count reaches 70% of the total (horizontal line) and is marked across both panels (red vertical dashed line).