High Concentrator Photovoltaics (HCPV) modules are typically equipped with multi-junction solar cells (MJSC) based on III-V compound semiconductors, which are typically either triple-junction (TJSC) or four-junction solar cells (FJSC). This work analyzes the impact of changing the number of subcells and their bandgaps in the optical efficiency. An exhaustive optical modelling is applied for estimating subcell short-circuit current density values under the concentrated illumination. The same typical concentrator of Fresnel lens plus a refractive homogenizer concentrator is applied to two different MJSCs. The optical efficiency when using the FJSC is 86.0%-almost 2% higher than with the TJSC. The acceptance angle results are similar for both cases, around 1.22°. Concerning the spectral matching ratio, SMR, the FJSC unit shows more distant values respect to the equivalent conditions to the standard illumination than the TJSC, due to the lower bandgaps of the FJSC.