False positive level in mass fp_M vs. spectral type for different numbers of points N_obs: 180 (yellow), 542 (orange), 904 (red), 1266 (brown), 1628 (green), 1990 (blue), 2352 (pink), and 3650 (purple), and for different OGS configurations (from top to bottom). Values of fp_M correspond to 1% of false positives and PHZ_med. The two horizontal lines indicate the 1 M_Earth (solid line) and 2 M_Earth (dashed line) levels for comparison.