I suspect that a part of the issue that Matt is highlighting might be related to the texture of the background, which appears to me to be some sort of a felt style of fabric.
In the first of the blue background images, and again in the last (grey) one, the texture of the felt can be seen.
While having the texture in clear focus shows that the image is in correct focus, as Matt has said, that is not the background's purpose. In cases such as this, where the subject is sitting directly upon the background, a flatter, less textured background surface might be the order of the day.
Otherwise, perhaps finding some way to elevate the subject off the surface and provide some separation between to the two items (how are your levitation skills, Dave
?) might help things along.