Multiplicity of red sources detected in mock maps. Average fraction of the 250 μm flux density emitted by the brightest galaxy in the Herschel beam is plotted as a function of total, single-dish 250 μm flux measured in our simulated maps. Horizontal error bars indicate the width of the chosen flux bin, while vertical error bars show the standard deviation of the distribution. The blue star refers to the study of Scudder et al. (2016), and the blue arrow indicates the observed trend they found towards brighter fluxes.