Issues with positioning parallax background in secondary viewport

Godot Version

v4.3.stable.official [77dcf97d8]

Question

My project is a multi-window platformer game which makes use of an invisible “main window” that hosts the world and multiple “sub windows” that, when moved, show a portion of the main window.

The issue stems from the fact that parallax backgrounds cannot be shared between viewports. Because of that, I have turned the background into a scene and instantiated it as a child of the sub window. While the buildings in the background work pretty much as expected, the background image seems to move with the sub window. When the window is set to fullscreen, the whole background looks as expected.

This is an example:

Windowed:

Fullscreen:

Ultimately, what I am looking for is the background’s position to be static and both the position and the scale to be relative to the main window. I suspect, however, that this might not be possible.

Can you help me determine whether this is possible to achieve and if so, how I would go about doing it?

Let me know if you need any other information about my implementation.