Unfortunately 'E' is I think a bit misleading because we also need to consider the ground time at LHR, or perhaps half of it, before the next flight. For example, if an aircraft is scheduled to arrive at LHR and then does nothing for a long time then even if the turnaround away from the hub is quick then that efficiency is lost at the other end.

I agree with mad_rich that the scheduling is something of a jigsaw that needs to be fitted all together in order to fully appreciate what is going on.