That value for “Static Lighting Level Scale” looks suspiciously low. In most situations you’ll want that value pretty close to 1. Unless the scale of your models is significantly different from Unreal Engine’s default (1 world unit = 1 cm) then you shouldn’t have to change this value significantly. If you change it to 1 what sort of change do you see with the blotchiness?
Also, just to debug, try turning off “Compress Lightmaps.” This will at least eliminate compression artifacts which can sometimes get in the way of seeing the true effect of what changes to the other values do.