Yeah, let's have a gravel surface one for the Wonder, since it's built by the player and is supposedly "maintained" by their people. And then we have a grass covered one for a map "ruins" object. 

Seems to work:  

This is an absurd comparison and you know it. On one hand, the Colossus of Rhodes fell due to an earthquake, and the Rhodians refused to rebuild it because of an oracle. On the other hand, the overgrowth of a kurgan with grass is a natural process that occurs in all cases if the monument is not maintained several times a year. In your example, the Colossus of Rhodes is completely destroyed. In the case of the kurgan modeled with grass covering it, it is still functional. We are comparing a natural disaster with an ordinary process. Furthermore a process that was difficult to stop.  A kurgan is not something similar to a Greek monument. First of all, this stone covering is not found on all kurgans. Multiple kurgans are simply covered with clumps of earth. One should not assume that it was standard practice to cover a kurgan with a stone shell. In fact, this is most common in certain regions. But even when vegetation had overgrown the gravel surface, this was a common occurrence in the Scythian landscape. Most of the kurgan mounds still standing were in this condition.  In any case, I’m not opposed to using a gravel surface. I also think it will look better. Once again, I’m criticizing a specific line of reasoning.

Perhaps reverse prop order in the structure's actor. 

Yes there was dirt decal texture, but for some reason it gets over the cobblestone, so i need to check if it is any vertical offset i can add to the cobblestone layer so it won't get undearneath the dirt one.