hmmm It looks that your GI radius is set too low, as you (apparantly, if I am not mistaken) get dark artifacts in the corners, (even with FG).
The photons are well distributed I guess, but imho the radius should be bigger, to smooth it out better.
I know nothing of the "photon volume accuracy and radius", so please tell us if you have something to teatch away regarding this setting. ( I never fiddle with this, as I have no clue at to how it works.)
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