The header background image is centered by default, and as it is a background image it has to fill the header/page title area.
You can change the focal point of the background by adding this CSS snippet at Customize > Additional CSS:
.entry-header.with-image,
.archive-header.with-image {
background-position: 85% center;
}This will move the focal point from the center to approximately where the main character is on your image. You won’t notice any difference on wide screens, but as the screen narrows on mobile, the main character should be centered.