Two different uniform thicknesses (8 and 68 nm) of a nanocomposite film comprising diblock copolymer matrix and magnetic nanoparticles filler have been installed in one sample preparation step under identical condition simultaneously. Long-range interface correlations are investigated. Maghemite (F2O3) nanoparticles covered with polystyrene chains are incorporated in polystyrene-block-polyisoprene to produce such film. The film is investigated with atomic force microscopy (AFM), X-ray reflectivity (XR), and scanning microfocus grazing incident small-angle X-ray scattering (GISAXS). The roughness of the substrate is replicated on the 68 nm thick composite film surface resulting in roughness correlation in a waveguide manner. No roughness correlation is observed in 8 nm film.