The interest for permanent magnet (PM) synchronous machines equipped with fractional-slot concentrated winding is more and more increasing in recent years. Among the others the Surface Mounted PM machines (SPM) have been widely selected from motor manufacturers. Particularly attractive are the spoke-type interior PM (IPM) machines. Nowadays, PM machines are often selected for variable speed applications without precise positioning requirements taking the advantage of sensorless control algorithms. Nevertheless the capability to detect the electrical rotor position without sensor also at zero speed, by means of techniques based on high-frequency signal injection, is an enhancing feature that requires a proper machine design. The aim of this paper is to evaluate the impact of both rotor and stator modifications taking a commercial motor as a reference geometry. The analysis of two rotor structures, SPM and IPM, as well as stator tooth geometry variations pointed out how the machine response due the injection of an high frequency voltage is significantly affected by the stator iron saturation. Finite elements simulations have been confirmed by test on two IPM motors manufactured with different stator design.