The skill "sundering blow" reduces monster resistence to 80%. This should lead to a 20% damage increase on primary attacks. However tests in C1 and C4 with mystic, abyss lord and squire are showing that the sphere is not working. The damage with and without the sphere is the same for primary attacks.
Steps to reproduce:
The Sundering Blow adds its debuff and the player does 20% increased primary attack damage to its target.