Location based opacity (fade out when no one in the zone, fade in when player inside)

Greetings, I have a question about how to achieve smth like this.
I have looked in to the - YouTube (location based opacity tut) and I like it very much. However, I need something a lilbit different from this tut. As the title says: fade out(custom zone/floor) when no one in the zone, fade in(custom zone/floor) when player inside. I think its smth familiar to the tut above, but need to be modified in the different way. Can s1 give a hand with it?

Why I need this:

I have a complex building inside of my level, which decrease FPS alot. Thats because of alot of modular floors with alot of props etc. Thats why I think the feature above can help me a bit to increase FPS.

Maybe I’m wrong and we have a better solution for this? Thank you!

Fading transparency in/out won’t help with FPS, unless you set the objects as entirely non-rendered.

Thank you. I have found allready that cull distance and levle streaming are my saviors.