Hi Andy,
Currently, it cannot be controlled in zero-span mode. It was possible at one point, which is why the controls exist. They will likely be removed in a future software update.
The Input Pwr setting will control the sensitivity of the BB60C. 0dBm being lowest sensitivity, -50dBm being the highest sensitivity. (in ~5dB steps) We suggest to set the Input Pwr setting to highest power you expect + 5dB. The displayed reference level is not tied to the Input Pwr as in sweep mode, so you can control the two independently.
It might be in a future update where you can set manual gain/atten globally, so it doesn’t need to be set in each mode. Maybe in a dialog that has controls relevant only to that receiver.
Let me know if you have further questions or comments.
Regards,
Andrew