The airflow under the wing flows slightly outboard as the wingtip vortex draws air from the high pressure area under the wing and swirls it upwards at and to the rear of the tip. I understood that to maximise cruise efficiency, you angle the outboard engine in a bit so that it is exactly in line with local airflow under the wing at cruise (for those aeroplanes that spend a long time in cruise). There is no point in having an engine that does not have a thrustline in line with the airflow at the engine location. Therefore, the inner engine is angled slightly less. Whatever, in turbulence, you should see them waggling and nodding whilst the wing is flapping up and down. Rather disconcerting.