Average transverse momentum of charged pions from PYTHIA 8 simulations as a function of self-normalised midrapidity multiplicity $\langle n_{\rm ch} \rangle$ (left) and of the self-normalised forward energy $\langle ZN \rangle$ (right) in the different multi-differential classes introduced in this work. Statistical uncertainties are shown as vertical bars, but they are hardly visible in the figures.