If both your StyleRef styles are numbered as part of the same outline number list then there is a way of nesting fields to achieve this. It works by comparing the autonumbers on the headings.

Let's assume that you are including Heading 1 on all pages and Heading 2 only if it sits under that particular Heading 1 level.
Set up the fields like this: the second one is nest of 4 fields.
{StyleRef "Heading 1"} - {If{StyleRef "Heading 2" \n} > {StyleRef "Heading 1" \n} {StyleRef "Heading 2"} ""}

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Andrew Lockton
Chrysalis Design, Melbourne Australia