How to add a new account if "User name" for authentification is not identical with "Owner" of calendar?

[taosxx]

In our organization, we have "personal" and "functional" caldav calendars we can access with the same user name and password but different urls.

A "personal" caldav url looks like this:
https://calddav.base.url/users/username@organization/calendar/
And the user name is:
username@organization

There's no problem if I add a new account for my personal calendars as "Generic login" - "Login with URL and user name" (I can even get away with using just "caldav.base.url" in the URL field). If I go later into the settings of this account it shows the correct "User name". Opening the details for the calendar also shows the correct "Owner" and the correct "Address (URL)". Everything works as expected.

Now I want to add a shared "functional" calendar.

A "functional" caldav url looks a little different:
https://caldav.base.url/users/function@department.organization/calendar/
But the user name to access it is the same as for the "personal" calendars:
username@organization
However, the actual e-mail would be:
function@department.organization

Whatever I try (complete url, only base url, combinations of username@organization/function@department.organization), if I actually succeed in creating an account (I have to stick to "username@organisation" as "User name" for that), I'll end up with a wrong "Owner" and "Address URL" for the calendar, i.e. exactly the same as for the "personal" calendars instead of the expected "function@department.organization" as "Owner" and "https://caldav.base.url/users/function@department.organization/calendar/" as "Address (URL)". And I use "expected" because I have an old installation of DAVx5 (installed maybe 5 years ago and updated regularly) which shows exactly that - and still happily syncs not only my "personal" but also "functional" calendars.

So, how does adding an account for a different url but same user name nowadays work?