The display mode is dependent on the aspect ratio of the used image in comparison to the area it is displayed in. The image is almost square while it needs to be displayed in a wide rectangle (the screen), leading to vertical cropping.
I suggest using an image with a similar aspect ratio as the area it is displayed in.
If you’re comparing it to Safari, on Safari we disable the special positioning and turn it into a plain background image because Safari has issues rendering images that are both cover-sized and fixed.