ImmersiveLayout image / headline position changes

Immersive logic might not be expected. E.g. in the article https://www.theguardian.com/lifeandstyle/2023/jul/04/how-we-survive-mauro-prosperi-lost-desert-raw-bats-urine

There was a change to some logic in `ImmersiveLayout` in #6762 which might have overridden some layout logic.

Intended style was 80vh for image (or nav + image?) @HarryFischer please confirm

@mxdvl has suggested when implementing fixes, consider using `dvh` which is the dynamic view height on mobile
https://caniuse.com/mdn-css_types_length_viewport_percentage_units_dynamic
https://developer.mozilla.org/en-US/docs/Web/CSS/length#dynamic