Running Header in FrameMaker — Subchapter Files Need Chapter Title

Hi all, I’m using a .book file setup where each chapter and subchapter is its own file.

Here’s the challenge:

• Each chapter file starts with a Heading1 paragraph for the chapter title.

• Subchapter files do not contain a Heading1 — just content that belongs to the chapter. Each subchapter is Heading2. Heading3, etc.

• I want a running header on each page (including in subchapter files) that displays the current chapter title.

I understand that the default running header variable (<$paratext[Heading1]>) only works within a single file, so in subchapter files it shows up blank because there's no Heading1.

What I’ve done so far:

• Added a cross-reference on the Reference Page of each subchapter file that points to the Heading1 in the related chapter file.

• Inserted the variable (<$paratext[Heading1]>) into the header frame on the Master Page.

• After updating the book, this works: the header in the subchapter shows the correct chapter title.

The tedious part:

I have to manually insert a cross-reference in every subchapter file, pointing to its chapter file. This works great, but it feels repetitive — like something FrameMaker should be able to handle more easily, especially across a book file.

My question:

Is there a way to make this cleaner or more scalable?
For example:

• Can I define a variable that’s truly book-scoped?

• Or set this up once per chapter instead of repeating it per subchapter?

• Or automate this somehow?

Any insight or best practices would be appreciated. Thanks in advance!