It’s been a while since I’ve played with VXGI and I don’t have it installed on my system right now to remember the names, but I think there is a couple of parameters near the end of that VXGI parameters list that will allow you to increase the contact shadow radius. It will also increase the amount of artifacts though, so it’s a trade off… You can also combine VXGI with amounts of HBAO and UE4’s default AO to enhance the indirect shadows. It’s also a good idea to include some artificial lights with shadows, it will give some depth to the scene. A nice trick is to limit the radius of those lights to a couple of meters only, so the real-time shadows won’t be calculated for the whole scene and you’ll get better performance.