Hello,
Yes, the HTF inlet and outlet design temperatures on the Power Cycle page are the solar field HTF outlet and inlet design temperatures from the Solar Field page. You can edit the values on the Solar Field page, but not on the Power Cycle page.
For modeling purposes in SAM, the boundary of the power cycle is at the solar field inlet and outlet. You can see this clearly in Figure 7 of Wagner (2011) "Technical Manual for the SAM Physical Trough Manual."
Those temperatures are for the HTF, not the steam. Under design conditions, the HTF enters the heat exchanger between the solar field and power cycle at 391°C, and leaves it at 293°C. Table 12 of Wagner (2011) shows the steam conditions at design.
As for the mass flow rates, in my tests using the default trough system for the physical trough model, the field HTF mass flow rate is generally higher than the power cycle HTF mass flow rate.
Best regards,
Paul.