CPV System Conversion Efficiency

We are modeling a CPV system vs Flat Plate at various locations across the US with a wide variety of Solar Resource availability in order to conduct a feasibility study. The real world efficiencies given by SolFocus for their CPV system is 30% module and 28%-29% for the system. We altered factors to get our module to 30% and then changed the wiring loss factors to 1 to optimize system array efficiency but still get a 3% drop to 27% system efficiency. By inputing values larger than 1 for the wiring loss factor we can obtain a greater system efficiency. Is there any other factors that alter system efficiency other than telling the model that our wires actually increase the efficiency (not possible in this day and age... yet)? We tried soiling derate factors but this did not change anything either.