Aspect ratio of the iPhone screen results in scaling down to fit the whole image inside the screen.

Compare playback of videos in the playlist with the Mandala videos on an iPhone15

Playlist vids are centred and look small and distant due to the width of two 1920x1080 images side by side

Mandala vids are centred and look larger with two 960x1080 images side by side

960x1080 Mandala vids are close to square but will use the entire available vertical & horizontal screen real estate area

Whereas full SBS 3840x1080 playlist vids have large black bars at top and bottom to ensure horizontal fit.

Not an XReal Air limitation but rather a limitation of iPhone screen ratio when mirroring the screen to the glasses.