Table in popup - cannot set context condition with different initiating model?

I have a popup initiated as the first action in a sequence on a pagetitle component button.

The only component in the popup is a table on a different model than the pagetitle.

When I try to add a context condition, I’m only given an option to pick one field (Id = Id)… as if the context and table models were the same. But they’re not even on the same object!

Why am I not seeing Field and Context Field (or whatever the nomenclature is) as usual with context conditions?