Masks and complementary science regions that retain fractional coverage of the sky, fsky, from 0.8 to 0.2 (see details in Sect. 2.2). The grey is the CO mask, whose complement is a selected region with fsky = 0.8. In increments of fsky = 0.1, the retained regions can be identified by the colours from yellow (0.3) to blue (0.8). The LR63N and LR63S regions are displayed in black and white, respectively, and the LR63 region is the union of the two. Also shown is the (unapodized) point source mask used.