Sorry for the late reply but I’ve been very busy.
I didn’t use any particular trick. Just the settings Koola used except I have only one directional light.
Here you can see a screenshot of my lightmass settings
I didn’t use light propagation volume or the GI from the post process volume (thanks for the tip, I didn’t know that was there:))
I use postprocess volume just to adjust overall brightness and stuff like that. No particular trick.
For the directional light, here are the settings:
Like you can see nothing fancy, no tricks.
I think the key is having big lightmap resolutions like 1024 or even 2048pixels, making good uv mapping for the lightmaps is important also. Be sure to have nothing overlapping.