It's pretty simple. It took me a couple runs to notice it, but I didn't see it posted anywhere on here so I figured I'd give it a go and share with the community.
All you do is when you get in the instance, locate on your map the room that will have the Unique monkies spawned in it. If one edge of the room is squared off (its really obvious) it's guaranteed to have the chest spawned in it. Pictures below.