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Recently we proposed a new technique for subsurface topography estimation in deserts and arid regions using dual-frequency Interferometric Synthetic Aperture Radar (InSAR). One of the main concerns was the use of conventional SAR focusing techniques for imaging the subsurface region which can result in significant image degradation and lower limit on the minimum achievable azimuth resolution. In this paper we demonstrate the different image distortion effects that can appear in scenarios where top surface is non-planar. These effects include geometric distortion and dispersion of the point spread function. We then demonstrate how most of these effects can be corrected through the application of an iterative approach using an algorithm recently developed for subsurface topography estimation. Using scaled model measurements under laboratory conditions and 3D simulations of actual top layer topographies it is shown that the correction algorithm renders better azimuth resolution, improved geometric projection and significant improvement in interferometric coherence.