Comparison of shallow and deep WSRT data with the same masking strategy. The color map and dotted contours are a single WSRT observation of Leo T butwith the frequency-independent mask used in this work. The black contours are from the full deep WSRT observations. The levels are [2.5, 5, 10, 20, 30, 40] × 10¹⁹ atoms cm⁻². The lowest contour is slightly less than 5-σ for the deep data and 1.6-σ for the shallow data.