Fog inside the cave

when I put the EHF in my scene for godrays at the entrance of my cave I got a problem. My problem is that the fog at the entrance is fine but when i go inside the cave it is not. how can I “tell” the fog to not be in the cave. I thought it was fine since the objects cast a shadow that is blocking the visibility of the fog but maybe im wrong or need to change something. hope you guys can help m

e.