Revise guidance on styling headings

src/styles/typography/index.md.njk

@@ -19,11 +19,11 @@ If you’re not sure whether you should be using GDS Transport, read the Service
 
 ## Headings
 
-Mark up headings semantically using the appropriate <h#> level HTML element and use a heading class to apply the GOV.UK styling. 
+Mark up headings semantically using the appropriate <h#> level HTML element and use a heading class to apply the GOV.UK styling. Style headings consistently to create a clear visual hierarchy throughout your service.
 
-The styling should reflect the hierarchy of the page. If your `h1` is styled as `govuk-heading-l`, your `h2`s should be styled as `govuk-heading-m` and so on.
+If your service has lots of long form content, use the corresponding size class. For example an `<h1>` should use `govuk-heading-xl`, an `<h2>` should use `govuk-heading-l` and so on. 
 
-You should style headings consistently throughout your service. Use `govuk-heading-l` for your `h1`s by default. Use `govuk-heading-xl` for your `h1`s when your service has lots of longer pages with multiple levels of headings.
+If your service has lots of [question pages](../../patterns/question-pages), short form content or pages with long headings, start with `govuk-heading-l` for an `<h1>`. But change it if your pages feel unbalanced – semantic and visual hierarchy do not always need to be the same.
 
 Write all headings in sentence case.