Question Is there any way to change lighting/lightmap resolution or fake a lower resolution?

I'm trying to have sharply pixelated lighting for a surface and can't figure it out. I've been messing around with real time and baked lighting for this.
In this image of a baked point light, I posterize the HSV as a post-processing effect to give the lighting this old aesthetic, however, if you notice, there's a clean ring effect with the light levels that surpass the image resolution. I want to make the lighting match the Base Map I have here before the posterize poster-processing effect.

So my question is, is it possible to change the resolution of a baked lightmap and real time lighting in Unity? Or do I have to make a custom shader to get this effect? And if so, is there any may to access lightmaps in shaders/Shader Graph, like maybe a reference similar to _MainTex? Or do I have to make my own lighting shader to get what I need?