Because lack of SDC on Dvina, I've wondering what is goin' on with tracking in heavy ground clutters... That's why I picked first mission from "War of Nutrition" (yo, it's sounds like hip-hop, baby!), and locked on damn "Mirage"-s with 5/9 batterie. Switched on 55 km mode (for worst clutter avoiding efect) but Dvina tracked them like bread'n butter even when I was not able to see them. I don't believe this is due the Dvina's ability to follow delta. Think we should dig deep in that.

Dvina can follow target, if it is invisible to the FCO.
The target should be visible to the Range and Angle trackers.
They indicator is displaying 5km mode only.

Try this.

Use Volhov, without SDC. When the target disappears because of heavy ground clutter, switch the indicator to 5km mode.
You will be able to see the target more easily...