The part of the XRR curves belonging to the graphene/Cu (excluding the points belonging to bare Cu) was fitted with a slab model using the Refl1D software. The slabs include Cu (bulk), C (single atomic layer), and a void in between. The fitting parameters are combined in Table . We define the interlayer Cu-C gap as the distance between the inflection point of the Cu slab and the center of the C layer, i.e., dvoid + dGr/2, where dvoid is the thickness of the void and dGr is the thickness of the graphene layer (C atomic radius) as illustrated in Figure . As we can assume from the fit results, the gap can be somewhat smaller for individual flakes: 2.09 ± 0.04 Å in the case of 300-400 μm flakes (the average size at the time when the scattering angle is around the Kiessig minimum at 0.8 Å -1 ), 2.15 ± 0.01 Å in the case of 1-mm flakes, and 2.21 ± 0.02 Å for the complete layer. The decrease of the separation by ~6 % for small flakes with respect to the continuous layer can be argued to be caused by the supposedly stronger interaction of the liquid metal substrate with the individual flakes. Indeed, the C atoms at the edges of the flakes "miss" C neighbors. They tend to share electrons with Cu, thus "chemically" binding to it, as opposed to the center of the flakes that undergo physisorption through van der Waals interactions. The resulting flakes are bent near the edges with edge C atoms being much closer to Cu than for an infinite layer. This also applies some stress to the center of the flake that moves slightly towards the underlying Cu surface. Indeed, for extremely small flakes, atomistic simulations predict the C-clusters to sink slightly into the Cu surface. The much larger value of the equivalent roughness of graphene in the case of smaller flakes might indicate the presence of a much larger dispersion of Cu-to-C distances. However, we note that the mentioned error bars indicate the 95% confidence intervals of the fit itself, whereas we estimate the total experimental error bar of the Cu-C gap as ± 0.05-0.10 Å based on the reproducibility. Thus, although our results show a trend toward a shorter distance for small flakes with respect to the infinite layer, the exact value should be treated with caution.