The simultaneous and disentangled presence of the specular reflection from the bare and graphene-covered surface can be used to measure the two corresponding XRR curves with one single conventional αi-2αi angular scan. In our previous work, we characterized the height of the graphene on Cu, also called the 'gap' between the surface of the liquid catalyst and the graphene layer fully covering the surface, as this parameter is related to the interlayer van der Waals binding force between the metal and the carbon layer. However, it is unknown whether the gap value is identical for isolated flakes of graphene. Therefore, we address this aspect in the following experiment.