you can use some tricks to improve it though
Distance Field Ambient Occlusion | Unreal Engine Documentation ← scroll down to Foliage
the gist is that for LOD1/2/etc you pull the vertices towards the camera to get them closer compared to the distancefield AO area, and for imposters you pull them towards the camera but on top of that you use PDO to push some areas back into the AO area to simulate a better volume