The premise of this so-called "theory" is that the observed object must vanish at some point. And the condition for that to happen is that the object must be further and further away, and in so doing it must become smaller and smaller, till at some point it is smaller than the resolution power of the eye, which at this point it effectively "vanishes". When we look at the rising and setting sun, does it get bigger or smaller? If it doesn't, then the simple conclusion must be it must be maintaining the same distance from the observer. Which means either the sun or the observer is travelling in a circular path.