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Internally, as from SR 2 or 3, I do not know exactly any more, Poser just ignores AO settings as soon as IDL is vinked On in renders settings.
So put AO where ever you want :-)

In Poser 9 and Poser Pro 2012 IDL can be combined with AO.

I've not tried doing what Blackhearted says but the idea makes a lot of sense to me - I'll certainly be giving it a go.

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