How to account for curses in pob

Good morning! I know that I can only use 1 curse unless I have a way to allow more.

I am current running Assassin's Mark linked with Arcanist Brand (and Frost Bomb), which I use on bosses or elites. The build guide also includes a ring with "curse enemies with vulnerability on hit", but there is no path to allow for a second curse. I was thinking of anointing my amulet with "Whispers of Doom", but I am not sure if the pob is properly showing me the damage change. I would lose the existing anoint (Arcane Potency, which adds a lot of damage), so I want to make sure that this is even worth doing. Is there a specific way to make sure that the pob is calculating everything properly, or does it automatically recognize when there is a second curse can be active, and the damage numbers shown are already correct? The reason I ask is because removing vulnerability from the ring in the pob does not change the damage numbers. How do I determine the true impact of vulnerability?

Already works well for this. You can see this: Have both curses in w/o Whispers and hover your mouse over the checkbox for each in the Skills section. You'll see the stronger curse will say you lose x% damage if you remove it while hovering over the weaker one shows nothing.