Effect of post-processing masking on the HI signal reconstruction for the oscillating beam. Left: Frequency power spectrum of the reconstructed HI signal. The solid black curve shows the true HI signal plus noise, and the dotted red curve represents the SDecGMCA reconstruction before masking. The dashed red curve shows the result after excluding problematic lines of sight, which suppresses the spurious peak and improves recovery at lower k_ν. Other methods are shown in lighter transparent lines for comparison, with minimum improvement observed. Right: Same as the left panel, but for the angular power spectrum of the reconstructed HI signal. The top panel displays the reconstructed power spectra from different methods, and the bottom panel shows the ratio to the true signal.