Senna and Soul Generation via Spoils of War

Senna's passive reads, "Small minions and monsters have a 20% chance to spawn Mist Wraiths, reduced to 5.5% chance on those that Senna kills." When Senna executes a non-cannon minion via Spoils of War (the gold generation passive on Steel Shoulderguards and Relic Shield), my testing indicates souls have a 5.5% chance to drop. Is this correct? Is this the intended behavior, or a design oversight?
Report as:
Offensive Spam Harassment Incorrect Board