sorry, but i don´t understand what you exactely want. if i create fullscreen websites with hype,
i used to have different layouts for different screensizes. there you can layout your fullscreen for every screen.
you can scale object proportionally, including content, or you can let images stretching, like what you want.
or let the images expand to fill. all you have to do is, choose the right pins for the elements
in the "Flexible Layout" - panel.
maby this is your answer:
I'm not sure there is anything "baked" into Hype. Hype does have a "shrink to fit" in the Flexible Layout section of the Inspecto. This effectively keeps the ratio when reducing the window from it's largest size. This way you could set up your document for the highest screen resolution and have everything shrink to fit. I'm not sure if this will work for your purposes.