Creating customised popup headers within a consortium

Folks,

I've read what documentation I can find on creating/managing popup headers and feel I'm reasonably okay with the concepts involved.  What I can't find is how, in a consortium environment, the relevant popup header is displayed to only users in our organisation.  

I'm wondering if it's controlled by the organisation name that's associated with the entry in T_DEFAULTS.

Can anyone clarify this for me please?

Martin