Ah okay... I'd half wondered if the black artifacts that can appear in IDL only renders were any relation to what you'd mentioned.

But I've since read an explanation from Bagginsbill on how these are linked to Irradiance Caching... and from what you're also saying above too, it doesn't sound like that sphere mapped node cheat would help with those black IDL pre-pass artifacts?

Still, very interesting relative to ray-traced reflections...

Many thanks