Yes, the feature is designed to operate only on your current position (and what you're doing) and I don't think it takes your plan into consideration at all. Certainly if you're nearing your destination you should see its frequencies, though, as by then it would be near enough.

During flight, the radio window shows FIS/Tower/nearby airfield frequencies in different colors. While approaching my destination or alternate airfield I get not information about the frequencies I have to dial in - is this intentional ?

-mike@edtg