1D radii (left) and $\lambda$ parameters (right) as a function of the cube root of the charged-particle multiplicity density $\langle {\rm d}N_{\rm ch}/{\rm d}\eta \rangle^{1/3}$ in the low $k_\mathrm{T}$ range compared with results obtained in Pb$-$Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV. Statistical uncertainties are shown as bars, and systematic uncertainties are shown as boxes.