Accuracy of Dish optical efficiency

I am wondering how accurate is the dish optical loss calculation in the Dish-Engine model. It appears that the Dish model is not as highly developed as the trough model. If there is any experimental field data available on dish systems, I would appreciate if someone could please point me to it.
Thanks
Ravi

The best source of information about SAM's dish-Stirling model is the Master's degree thesis by Fraser, P. (M.S. 2008), "Stirling Dish System Performance Prediction Model," which you can download from the Reference Manuals page:

/performance 

Best regards,
Paul.