So this is happening to multiple OBJ files that are coming from more than one source? Does this happen to every single OBJ you import into Daz Studio? If you tried every one of the listed program configurations, one of them should have at least worked size wise. I referenced Blender just to state that I have to use a large scale increase, 5000%, for it to be the proper size for my imports. Some of those listed program formats that Studio offers though are even larger in scale.

The only other thing that I can think of, and it may not be related because it doesn't have to do with size... but you did mention "non-existent"... and that is that sometimes you need to go to the surfaces tab and adjust the "Opacity Strength" in the shaders to 100% to make the model visible. For some reason, some of the OBJ files are imported in to Studio with the opacity set to 0%. I've even had this happen on OBJ files I purchased here on Renderosity. Again, this might not be the issue, but it is the only other reason I can think of that it would be non-existent on import.