I think they help define it as a mine. How much space they take up determines how much cover they can possibly provide, so if you want no cover keep them small, if you want them to add tactically rather than just aesthetically make them larger. I don't think they look bad now, but some of them are far enough off from each other it makes it look like they've twisted, so you could add a few that have fallen down partially blocking passages and what not to integrate them more with the map.