Time average of log ϵ_ff at 250, 500, 1000, 2500, and 5000 M_⊙ pc⁻² in the various simulations. The data have been slightly displaced to make the comparison clearer. The different markers highlight different axes of projections, and the error bars show the dispersion of ϵ_ff measured at a given column density due to its evolution across the simulation. The effects from the line of sight and stellar feedback are not enough to overcome this dispersion, such that in a set of clouds at different evolutionary stages they will not be visible if the dependence from Σ_avg is not taken into account.