Recently, a 3-D SAR imaging technique based on Compressive Sampling (CS) has been introduced . It allows to noticeably decrease the number of acquisitions required and to obtained an increased elevation resolution. The number of acquisitions required to obtain a reliable 3-D reconstruction is related to the desired resolution and to the overall elevation extension of the scene. If the number of measurements is not sufficiently high, artifacts can appear in the reconstruction. In this paper, this issue is investigated on COSMO-Skymed simulated data.