When a workspace line references its parent, the naming of that parent should match the parent level, not the workspace level.
By not reflecting the customized terminology we are introducing layers of confusion for the team members who don’t spend their entire days working in Aha! – they will struggle to differentiate the level that they need to map to.
I would add to this that the UI should also be able to do the same for the child record. At the product line level you will see both the parent and the child at times, and both records are referenced using the product line terminology.