In GPR prospecting, strong reflections due to the background material interface can hinder the detection of localized buried scatterers, especially when the targets are close (in terms of probing wavelength) to the interface. Moreover, signals due to objects located outside the investigated domain and occurring in the observation time window may dramatically affect the reliability of the results. In order to mitigate such kind of clutter, an entropy based approach has been recently proposed in the frame of intra-wall diagnostic. In this paper, we assess the performance of such an approach by processing experimental data collected in laboratory controlled conditions and referred for the challenging situation of shallower dielectric and metallic targets, whose back-scattered fields overlap in time with the air-soil interface signal. In addition, a performance comparison of the proposed method is performed with other two approaches, i.e., the mean subtraction method and the subspace projection procedure.