Ireland seemed to be the nearest player to Rooney other than Boyata who seemed to be designated the near post area as it was him who was beaten there previously when Given made the fantastic reflex save for the corner; so I think it's safe to say that near post was Boyata's zone.
Imo there's no way Ireland was supposed to be in charge of the centre of the 6 yard box & whilst some keepers would have punched that ball out, no one in their right mind would have a policy of allowing the opposing CF to attack the space in front of the keeper unchallenged, therefore I recon it's safe to assume the other CB should have been there.
So imo the bloke most at fault for Rooney's goal was Vincent Kompany.
That's assuming we still operate a zonal system after the initial set piece has been taken. Mind you it'd still be Kompany's fault then for not marking him anyway. Pretty piss poor show either way.