Confused about HDRP light settings

I just transferred my project to HDRP for having more controls over the light, but setting up the light is very confusing, even with the tutorials and youtube videos.

First: the ceiling indoors never matches the walls in color, even when they share the same material. This has to do with ambient light and reflection as I know now. But there seems to be no way to make it look like its a uniform lit room with walls and ceiling made in one piece. You can see the walls and ceiling in the pics below. I searched for hours, but I cant find any real solution in the web to this particular thing.

Second: I set up the sun as said in the tutorial, giving it 100’000 lux strength for a noon sun. Then I adjust HDRI sky settings to have a natural looking light. But I need to set the intensity multiplier to 10’000 to achieve that (is that a normal value?). How can I have a natural bright sunny day with uniform lighting indoors as outdoors with a nice blue sky?

Also, all lighting is realtime, as baked lightmaps look terrible with the static tiles I use for all architecture.
Some advice how to learn to rule the settings would be nice.

100’000 lux sun & 10 HDRI sky intensity multiplier:

100’000 lux sun & 10’000 HDRI sky intensity multiplier: