My bad - turns out 3D Rad only supports vertex based lighting (@tinsoldier explains the poor lighting artifacts in older versions of 3D Rad), never seen that kind of blending though. What's looking like the GI could be a result of the Fog object but the details farther to the camera don't really seem greyish, they're kinda black. I still go for Godot (The latest, Godot 3.1).