Terrain Tree view distance

Hi so I didn't use the tree creator, I made my own trees in maya 18 varieties

Problem is when I use the terrain tree brush the tree view distance is pathetic... but it is pretty much impossible for me to manually place 18 trees around the entire map at a density for it to not look like a crappy dead map

I tried looking all over and people say the distance of the trees is hard capped by unity Which is stupid but is there a script or way that I can place my 18 trees randomly around the map? a bit like the pain brush tool can do but without the stupid fact that trees vanish after a 10 second walk