As I learned from the 'Combining Concrete Paving and Grass' tutorial, I tried something different.
Because I don't have Railclone with me, I tried using everything in Forest Pack.
Here's what happened:
First I attached multiple pavement concrete model into one editable poly and also merge grass models in the scene.
Then I scatter the pavement concrete to the area I want. (These pavement concretes are actually one forest object)
Scatter the grass to the whole area
now select forest object as an exclude
Doesn't comes out as you think, does it? haha.
Try increasing the resolution.
Nope. Doesn't help.
Maybe, try changing the 'Boundary Checking' to 'Size' and 'Edge'
Doesn't help either. Anyway to fix this?