The size of the content displayed in the fenced frame looks different between desktop and smartphone.
You can check by protected audience demo page.

Desktop(120.0.6099.129（Official Build） （x86_64)

Smartphone in devlopertool(120.0.6099.129（Official Build） （x86_64)

Real Smartphone(Android 14; Pixel 7. Chrome 120.0.6099.144)

Is this behavior intentional? I believe the behavior in Desktop is correct.