BP for fog in one zone only

I have a zone in my level where I would like to have different settings for the fog.
I have created a blueprint with a timeline and a trigger box so that when the player crosses the trigger box the fog settings smoothly changes

however if the character goes back before the zone the fog doesn’t change back to what it was. How could I create a blueprint along the lines of: if player is in this box (that would be the whole zone) the fog= this density and color and if player leaves the box fog= this other density and color
would it be a huge trigger box ? how would that work

I’m not very good at blueprint

thank you

Perhaps not the solution you are looking for exactly. However, you can use post process volumes to render materials. In this case you can render a fog effect with control in certain areas: Elias Wick | Fog. The effect is bound to the volume and can transition nicely with feathered bounds.