I’m not sure that would be the case. If it’s software, then all indirect lighting is solved with the SDFs, which are created out of the mesh, but aren’t the same thing as the mesh. If it’s hardware, it would automatically generate a proxy mesh with a lower polycount, so unless the proxy mesh and the nanite mesh are very different, there shouldn’t be a problem.
My guess? If you’re working with the preview build and have lumen with landscape, there tend to be some relatively strong artifacting if you intersect with terrain. The reasons for this are very complicated and I only loosely understand it, but the landscape traces are offset by a certain amount to avoid self-intersection, and there’s a possibility that your small mesh sits inside of that offset, causing the trace to avoid part of the mesh. It would get worse as you get further out because the landscape would be tesselating to a lower LOD, and screen traces would catch less and less of the mesh to hide the artifacting.
Essentially? I’m not sure you’ll be able to intersect the mesh with terrain on this current version of lumen without problems. That being said, I also don’t have all the information, so if I learn more, I might be able to help.