Alan,
iModeler does not support cross-posting between group or between headlines and groups as you describe above.
A good general principle is that we'd like all type of stuff suitable for the Headlines to be posted there. So if you are in doubt - have kind of material that would suit a group and the headlines - I'd suggest to go for the headlines. Thus The Halifax article is definitely where it belongs.
If you like to post something about it i a group, I'd suggest simply linking to the original headlines article from the group post.
Hope this helps.