In MR you have another way of setting up AO. There is the default feature like you illustrate (put a AO shader in the diffuse slot), but the second one is pretty neat. It only creates AO where there's no direct light and gives a realistic approach of using AO because it only appears on indirect illumination spots. This can be found under the "special effects" tab of the A&D shaders.See attachment for the difference. It would be very nice to see such a feature for AO in Corona.