Comparison between the 3D clumping factor (black shaded area) and the clumping factor reconstructed using equation (2) in the gadget-3 sample (blue; Bonafede et al. 2011; Roncarelli et al. 2013). The red shaded area shows the 3D ‘residual clumping’ obtained by cutting out the densest gas cells (see Roncarelli et al. 2013).