Hmm, never played with the attenuation setting on the lights before. They were on constant which seems to be the default. I take it the inverse square setting causes the light to fall off more with distance? So instead of the corners being dark due to light not having enough bounces to get there, they are dark because the light has fallen off with path length. I will have to remember that.

I did have to triple the intensity of all the lights (which makes sense), could probably have gone even higher but that at least let me crank up the exposure without adding too much noise. Also doubled the number of samples. But I see what you mean. The eyes are particularly improved (do emissive materials in superfly attenuate at the inverse square rate too?). I tried the denoise again, and while it completely removes all the noise, even at 50 samples here it seems like it is erasing too much detail. Can't complain too much about the number of samples though, it was still only a five minute render with optix.