what is the design point used by SAM in "CSP molten Salt Power Tower

my following question are about the "solar multiple",the"Design Point" and the "calculation of mirror surface needed".
when I use "CSP molten Salt Power Tower" to simulate a 50MW tower case,i have found that SAM seems use the summer solstitial solar noon,may be 12:00 of June 20th.
since the SM(design point)=Q(th,solar field)/Q(th,power block),my question are

1.is SAM use this SM definition? Q(th,solar field)is the energy arrived on the receiver surface or the receiver thermal output?

2.in hourly results,i think "Solar field optical efficiency hourly" is "the energy arrived on the receiver surface" over "the energy arrived on the mirror surface", that is to say,the efficiency includes Field availability,Incidence cosine,Shading and Blocking factor,‘Spillage’ or intercept,Atmospheric attenuation with distance, etc.am i correct?
why according to the hourly results,my calculted mirror surface differs from SAM's result?

3.what is the design point used by SAM in "CSP molten Salt Power Tower"?or how does SAM calculate the mirror surface needed?

Hello Paul,

I would like to know to which extent that SAM consider the atmospheric attenuation between the heliostat field and the central receiver? is SAM applying any factor?

Thank you.

Thanks for your response, Paul.

I have read section 2.1.1 and I suppose that SAM is using as a basis the Solar II visibility conditions, no matter the conditions of the plant, is this correct?
In that case, can these conditions be changed?

Thank you.