This value is added to the LOD Scale of each Mesh Component. Negative values will lower the overall density/resolution or the vertex grid and make the LODs smaller, higher values will increase the density/resolution and make the LODs larger. Smallest value is -0.5. That will make the inner LOD as tight and optimized as possible
Usage
r.Water.WaterMesh.LODScaleBias [value]
Set via the console (~) or in DefaultEngine.ini / DefaultGame.ini.