Full-page images in eBooks may not always appear perfectly centered or fill the entire screen due to the way e-readers handle image display. E-reader devices commonly incorporate a pre-set margin or gap around all content displayed on the screen.
Additionally, since various e-readers come with different screen sizes and ratios, images are adjusted to fit within these dimensions to prevent any cropping or loss of image content. This adaptation to diverse screen sizes might result in varied gap sizes around images on different devices.
However, this behavior is a standard feature in eBook publishing, as creating a single image size to perfectly fit all device screens is not feasible due to the varying screen ratios across devices.