Is post-processed fog of war possible for a turn-based tile-based project?

Hello! For fog of war, first I tried placing a black plane mesh over the level and making it transparent depending on data it receives from a render target. It almost works, but the challenge is that because of the isometric camera angle, you can often “peek” a significant amount below it.

I’m now trying to map the render target onto a post-process material, but I’m struggling to make the fog of war stay still–as the player moves around, so does the post processing material, almost like it’s swimming around the player. I’ve been working for days at this and I don’t know how to securely affix that post-processing material to the worldspace.

Let me know what you think. I can provide more details. Struggling a lot with this one!

Here’s the material graph

And here’s the result