The environment HDR used in the Sky can’t be scaled but the viewport camera lens length can be changed to allow you to see more of the background. With that said, I wouldn’t use the HDR as the visible background. These images are 32 bit and composed of multiple exposures. They light the scene with much more luminance than a standard 8 bit image but can have stitching errors, they also have to get tone-mapped down to 8 bit to display on the screen. For this reason, I’d use an image of the specific background you want in the visible background.
Of course some HDR’s will have more stitching issues than others and ones shot on a tripod with a special head will be cleanest. I actually shot this one handheld on a hike and not to make excuses but it was pretty windy!