I don't know about Marvin or iOS, but perhaps the new version can't handle covers as high as the old one could.
Although I would think it should first fit the height to the page, and then calculate the needed width.
Increasing the width means the height is now smaller in comparison -- when using cover aspect ratio, you can also think of the new cover as 400*533 pixels.
Less pixels to squeeze out the bottom and onto the next page.
