  We discuss a rigorous procedure for quantifying the difference between our
past lightcone and the past lightcone of the fiducial
Friedmann-Lemaitre-Robertson-Walker spacetime modeling the large-scale
description of cosmological data in the standard $\Lambda\mathrm{CDM}$
scenario. This result is made possible by exploiting the scale-dependent
distance functional between past lightcones recently introduced by us. We
express this harmonic map type functional in terms of the physical quantities
that characterize the actual measurements along our past lightcone, namely the
area distance and the lensing distortion, also addressing the very delicate
problem of the presence of lightcone caustics. This analysis works beautifully
and seems to remove several of the difficulties encountered in comparing the
actual geometry of our past lightcone with the geometry of the fiducial FLRW
lightcone of choice. We also discuss how, from the point of view of the FLRW
geometry, this distance functional may be interpreted as a scale-dependent
effective field, the pre-homogeneity field, that may be of relevance in
selecting the FLRW model that best fits the observational data.
