Baked AO on Mobile renderer: How to make LightmapGI actually darken corners?

Been trying all day to get some decent lightmaps baked for a mobile game I'm working on, but the corners just look completely flat and washed out.
Since it’s a mobile game, I'm using the Renderer as 'mobile', so real-time SSAO is not possible. I strictly need to bake that nice contact shadow/darkness into the lightmaps.

I'm using Godot 4 and baking with LightmapGI on high settings. Is there a specific trick to forcing Godot’s lightmapper to give deeper corner shadows, or should I just give up and bake an AO map directly onto the textures in Blender?

The map was made using CSG nodes then baked them into MeshInstance3Ds and then ran 'Unwrap UV2 for Lightmap/AO' on them.

Any help is much appreciated!!! (its been all day)