A high-resolution dynamic response is important for characterizing a system's dynamic properties. Measurements involving a limited number of points on the structure can be expanded to unmeasured points through approximation or model-based expansion techniques that rely on the introduction of a numerical model. Recently, an expansion method called System Equivalent Model Mixing (SEMM) was proposed where a numerical DoF set is used to extend an experimental model with limited measurement points. The concept of SEMM is similar to the well-known SEREP and VIKING expansion methods, but it is defined in the frequency domain. Using the dynamic substructuring approach, the equivalent experimental and numerical models are coupled so that the hybrid model inherits the dynamic properties of both models. Although the method has been well adopted, there is still no comprehensive phenomenological analysis to determine the influence of the method's parameters on the consistency of the hybrid model and thus on the accuracy of the expansion process. This paper addresses the issue by evaluating the accuracy of the SEMM expansion process, focusing on the influence of the regularity of the so-called equivalent numerical model. The introduction of quasi-equivalent numerical models into SEMM is analysed here, which can differ not only with respect to the mass and stiffness properties but also in terms of the geometry and boundary conditions. The parametric study was carried out on a real component of a household appliance, and the most influential parameters in terms of accuracy of the SEMM expansion process were identified. The analysis showed that accurate expansion results, with a small number of experimental points, is achieved if only those points are well scattered across the analysed system.