The OSD sort of accidentally does this. 👀
If it dumbly detects that only a single assignment is present on a fader then it'll show the assignment's name, whereas if more than one assignments are present it'll show the fader's name.
For most people, the fader's name is always shown as this dumb check also counts any inactive assignments (e.g. apps that aren't open, old app
.exes, old devices, or old plugins).
The "Extendable OSD" milestone is one that should make this behaviour a tad more customisable.