Belt corruption "increased area of effect" has no effect

Playing rf chieftain in crucible league. I swapped out my regular immortal flesh for an immortal flesh belt with 10% increased aoe and 14% increased skill duration - the increased skill duration applies (confirmed via lifetap duration in fire trap tooltip), but the rf AoE doesn't change at all.

I confirmed that it's not a case of the aoe increase being unnoticeable - I used a pillar of the caged god staff (with my char's 81 intelligence) to confirm that even a 4% increase in AoE should be visible, so it looks like the increased aoe belt corruption is just not applying at all.

Screenshots attached show belt being equipped and unequipped with no change in RF aoe.