I played a bit with this (would be the same for iClone or CC) and it requires changing the setting of the spotlight you are using for Iray and also cranking up its Intensity in iClone.
In iClone I set the Multiplier for the spotlight to 5.0.
In Iray I have the following settings:
The trick for sharp shadows in Iray (which you need for the mask to show) is to have a light source with a small diameter. But the light will be fainter so the Intensity Multiplier needs to be increased.
This should help.
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