CSP Receiver incident thermal power - SAM and SolarPILOT

To validate my model, I'm trying to use SAM with the same input parameters as mine. I'm getting the receiver's flux profile from SolarPILOT. Even using the same location, heliostat field and geometry, the resulting incident thermal power (MWt) in SAM is exactly 21% greater than that obtained by integrating the SolarPILOT profile over my receiver surface. I would like to know if there is any way to understand this difference, if it could be some parameter like re-radiation or optical variation in sun's rays. 
In both cases (SAM and SolarPILOT), the location is Seville, with a receiver measuring 12.92m high and 10.59m in diameter, field with 3685 heliostats, tower height of 143.3m, and molten salt as fluid. Using 21% higher incident flux, my results would be the same as those provided by SAM, so I'm not sure. 

I'd like to apologize for this topic. I found out what the problem was. It was related to the calculation of tubes per panel between my model and SAM's, which is based on Wagner's thesis. If possible, I'd suggest to add the information of resulting number of tubes per panel in CSP Tower at SAM.