Answer: Dog must stand outside the focal focal of the concave mirror.
Explanation:
In concave mirror, when ever an object is placed between the focal point and pole the image will be formed behind the mirror larger than the size of the actual object.
When an object is outside the focal point of the mirror then concave mirror will form a real and inverted image smaller than the original size of the object.
So in order to appear to be sitting the dog must stand outside the focal length of the concave mirror.
