Hello :) I think I've found a bug with the latest beta (9.4.2017).
If you set up an AO shader and you play with the Max Distance parameter it works fine. Unfortunately if you slot in a texture map in the "Max Distance texture" slot then the Max Distance parameter doesn't work anymore - it literally has no effect at all.
Contrary, in 3ds Max, you can still use the Max Distance parameter to define the radius of the AO effect but it uses the the "Max Distance texture" as a mask.
The current workaround I am doing is to set the mix mode of the "Max Distance texture" to multiply. That then lets me control the radius as well as the mask for the AO.
Over :)