If not using fog, then mips should work, but it is a little tricky.

First of all, mips can be adjusted by either

mip_flat or mip_shaded variables.

I think it goes from 1 - 10 and when you do this, then you will notice that up close the terrain looks clear, but at a distance it gets blurry.

Also, if everything looks too clear at a distance, then the frame rate can drop.

But, I think these types of adjustments also depends on the size of the terrain too in WED. It seems easier to make a small terrain clear, than a large terrain does.

Also, terrain skin size is a factor.