New to UE4 lighting. Need advice on lighting

Hi everyone. I’m getting into unreal and looking for realistic lighting setup for my scene. I got some question regarding the lighting and shadow.

In this scene, i have directionalLight (moveable), skylight (moveable with daylight cubemap) and exponentialHeightFog. Very basic setup.

Problem i’m having is shadow under indirect lighting. The tree pieces on the bottom left cast no shadow on the ground without AO since both they and floor already have shadow cast by tree.

My scene is filled with shadow too dark to increase contrast in Post but some part are too bland (see fern on the ramp, very detached from the grass/dirt surface like bad photoshopping).

Any advice is much appreciated

Lighting with AO
Lighting without AO
Lit with AO
Lit without AO


this is hopefully helpful

best regards