I don't think tagmanager actually handles parameters as such, it handles the whole argument list as a single string IIRC so you can't access the parameter names.
Ah, ok, maybe I misunderstood the question - if it's about extracting arguments as separate tags, this is just about enabling this feature in Geany but it needs some extra work on Geany side which hasn't been done yet.
Geany (and ctags??) has no way of specifying scope for these because the scope is lexical not named like structure and class members. So they appear everywhere, not restricted to the appropriate function.
The scope is actually included correctly, we just don't take it into account and it has to be fixed at various places (should be pretty easy).