Effect of masking on the CO-only PS. The range of PS between the “low-contamination” and “high-contamination” models (Sect. 2.3.2) at k = 0.02 − 0.32 Mpc⁻¹ for CO lines (blue) is shown in relation to the percentage of voxels masked within the LIM tomographies for the frequency ranges of 225 ± 40 GHz (associated with z_[CII] = 7.4), 280 ± 40 GHz (z_[CII] = 5.8), 350 ± 40 GHz (z_[CII] = 4.3), and 410 ± 40 GHz (z_[CII] = 3.7). The lines represent the optimal CO masking sequence for our fiducial model, while each point and label indicate the J_up and subsample (“b” for “bright” and “c” for “complete”) associated with the masking array applied. The same masking sequence is applied to the “low-contamination” and “high-contamination” models (Sect. 4.2.1). As an illustration and assuming at this stage that the mask does not affect the [CII] PS (but see Sect. 4.2.2), we show the fiducial and range of [CII] PS predictions in red.