Processing has absolutely nothing to do with anything.
The cost is render calls.
Render calls are determined by the number of landscape components.
The bigger the landscape, the more components.
2x2 is less components than 1x1 so, half the draw calls roughly, and should be the first choiche for large scale things unless you know you need smaller tiles for occlusion (canyon maps).
Whatever settings or scale is applied, the cost of each component is pretty much set in stone, and only worsened by landscape materials.
Changing the LOD distribution can help a bit with tris heavy scenes, but chanches are none of your scenes are that heavy on tris count for it to matter.
In comparison, if you were to create static meshes that were properly optimized for occlusion, you would always get a better result…