At first hitting tab (PC's cancel) would send them to their pickup... but it turns out that actually just dismisses them to their previous location, not their default one. (It's just that their previous location IS their default one, if you haven't send them anywhere else.)
Having companions with no personal ties to their old locations or with ties to me personally (Codsworth and Dog being non-spoiler examples) stay in my home settlement is fine. But some of these companions have their own jobs! In their own cities! I tell them to stay at my settlement while I run a quest for someone else so I can pick them up on the way back and now they won't leave, even though we're not hanging out anymore.
How can I send companions back to their regular positions? Why will they never leave?
Is there a way, or is this something someone will have to mod in....?