Autonumbering 'format' not showing in TOC (Structured FM 2022)

In my strucutured document, I have a ChapterTitle element with conditional formatting:

• If the 'ChapterType' Attribute = "Prologue", the Autonumbering is "Prologue".
• If the 'ChapterType' Attribute = "Epilogue", the Autonumbering is "Epilogue".
• If the 'ChapterType' Attribute = "Chapter", the Autonumbering is "Chapter <$Chapnum>".

These are working as expected in the document.

However, when I generate the Table of Content, the Autonumbering isn't picked up - I only get the page number:

When I look at the Reference Page, it has the following:

This makes sense as there isn't any actual text against the element. What I'm actually after is something like this:

I am stumpped as to how to achive this. Replacing <$elemtextonly> with Chapter <$chapnum> works fine for those documents where the ChapterType Attribute = Chapter, but not for the others.

How do I have the TOC pick up the full autonumbering text?