I have a question about the correct practice to make a fading level border.

As you can see in the image, there are level tiles on the upper half (with normal collision polygons) and black (light occluding) tiles at the bottom. My goal is to make the blackness of the black tiles “creep” upwards into the level tiles so I have some sort of black fading out at the border so that the tiles won’t look so rough (and also ignore/override lighting from the level). For this exact setup, I only used a Tilemap, a PointLight2D Node from above and the collision + occlusion features for specific tiles in the Tilemap.

I tried using shaders, however I noticed that each shader I used was self contained in its own cell and could not go past the border to another tile. I am open to any approaches even outside the scope of a tilemap, but it should work dynamically with any new tiles placed afterwards.