Damage calculation for Invigorating Beam

[algoth]

Does anyone know how damage is calculated for Invigorating Beam? It states your "ranged attacks now do necrotic damage" My question is if you have a Staff or Orb that does Fire damage as the base and have gear that buffs fire damage by 10% and gear that buffs necrotic damage by 15% does your ranged attack get the 10% from fire or the 15% for necrotic or both? It should be noted that on the stats page it only calculates the fire bonus percent to the fire damage.