The obligation for the one who can see the Kaaba is to face its center; this is certain due to his ability to do so. The obligation for one who cannot see the Kaaba, whether far or near, is to face the direction of the Kaaba; because obedience is according to one's capacity, and this is the correct view. The direction of the Kaaba is such that if a person faces it, he is facing the Kaaba or its air. This is clarified - and the clarification is that if a line is drawn from his face at a right angle to the horizon, it would pass through the Kaaba or its air - or approximated - the approximation is that he is slightly deviating from the Kaaba or its air in a way that does not completely eliminate the facing, such that some part of the surface of the face remains facing it or its air. See: Maraqi al-Falah, pp. 212-213.