I still haven't gotten Diamonds in Layton Lake, it's true that area seems more difficult than other DLC areas. Now that I look at it, I haven't finished exploring the entire Layton Lake map, the maps are quite large.
Have you been able to get Diamonds in this reserve?
I think once I got a diamond Whitetail here, only once. In the initial days, I searched for a lot to get a diamond bear but couldn't find it. One day, I will get one for sure.