Hello,
Sorry for the delayed response.
The image is working as a background image, and it will not be visible in fullwidth with all device resolutions.
But there is some property values may help to get the view better. So you can try this code in your custom CSS:
.overlay-background-image {
background-repeat: no-repeat!important;
background-position: 50% 50%!important;
background-size: cover!important;
background-attachment: inherit!important;
}
Note: Path towards custom CSS: Extensions>Templates>Styles> Click on your current default template name then choose Template Options. Then find custom CSS within the custom code.
Best Regards