Terahertz (THz) inspection is a versatile tool for the non-destructive, quantitative characterization of conductive thin-films, including 2D-materials such as graphene. In this work, we apply high-resolution THz near-field transceiver probe-tips for the inspection of graphene-layers in reflection-mode. By taking advantage of the additional interface-selectivity of the reflectionmode not available in transmission-mode, we can now directly discern substrate- from top-layer inhomogeneity, which is important for the reliable 2D-layer characterization on inhomogeneous substrates.