I am not going to tell you it isn't the easiest thing to do. I just view that when you give players terrain to work with they should expect we will find the most advantages parts of the terrain and use them in our favor. In they wanted us to stand and fight the boss on the same general area as the boss they should have used the terrain to wall us in with the boss. Generally the idea is don't give enemies terrain players are not allowed to go to, and don't make your terrain just for visuals but for gameplay as well.