Mean intergalactic separation in Flagship (blue colours) and GAEA (green colours) simulations for all considered models (m1 and m3 for Flagship, ECLH and ECLQ for GAEA). For each model, the fiducial galaxy selection based on the Hα flux (Hα) is compared to the stellar mass-based selection (M_*). Shaded regions correspond to the standard deviation across five mocks for each model. Dotted and dashed grey lines represent the corresponding redshift uncertainties converted into distances for Flagship and GAEA simulations, respectively. GAEA models show smaller differences between each other and compared to the Flagship simulation models, in particular for the Hα selection of galaxies. Above z ∼ 0.9, the Hα selection follows the selection more closely, based on stellar mass for the Flagship simulation, with respect to GAEA.