Reconfigurable Intelligent Surface is a promising technology for the up-coming sixth-generation (6G) of cellular communication networks. In this context, an experimental study of specular and nonspecular reflections of a reflective surface by scattering parameter measurements in the 300 GHz range is presented. Here we compare the insertion loss of a fixed and passive reflective surface at its optimal output deflection angle with respect to the specular reflection on a metallic plate. We propose a methodology to assess the losses induced by the surface and validate the use of the device within a THz link. At its best, around 290 GHz, the surface insertion loss is less than 3 dB compared to the metallic plate. We then investigate a nonline-of-sight THz link operating in QSPK and QAM-16 coherent transmission using the reflective surface. Data rates up to 10 Gbits/s for QSPK and 20 Gbits/s for QAM-16. This is, to the best authors knowledge, the first demonstration of a non-line-ofsight THz data-link including such reflective surface.