Dear Pro. George, Many thanks for your detailed and clear exposition, which gives me a more clear idea about this question (Although I still don't really understand the basc mathematic things behind it).
I rechecked the sharp logs, and found that the original SAD sites were wrong, which had to be turned to its inverted ones for calculating the final density (while the SIRAS sites are correct, the final density was calculated directly from the original sites). And the SIRAS sites matched the Fo-Fc quite well~~~ Thanks, Pu
