I’m out at 1,000,000 x 1,000,000 and attached meshes to my skeleton don’t shake anymore. I used #define UE_LWC_RENDER_TILE_SIZE 128000.0
1048576.0 /* Maximum distance representable by a float whilst maintaining precision of at least 0.0625 units (1/16th of a cm) - Precision issues may occur for positions/distances represented by float types that exceed this value */
So 2097152.0 would be 1/8th of a cm at max tile distance. Which is way too loose for what we needed.
Seems that TILE_SIZE does some form of offset/rebasing:
float3 Offset = (LWCGetTile(Lhs) + LWCGetTile(Rhs)) * UE_LWC_RENDER_TILE_SIZE + Lhs.Offset;
The render side of things is still using floats.