Not quite. The Irradiance Sample Size is certainly used by IDL. I haven't investigated how AO works, since it seems to be turned off if IDL is turned on; ISS might be used by whichever is turned on. I don't think ISS makes sense for reflections, but that's a guess at this point.

On the other hand, so far I've wound up with ISS set at its highest value where it has little or no effect.

Whichway