1. Start the editor
2. a) Set a heavy fog - place an enemy 300m in front of you in a clear area - make sure you have no kind of visibility - They will spot you the same.
b) Go to a vegetation place - Place an enemy 100m with a dense bush ( like those cane kind of bushes ) between you and him - they will spot you the same as anything where between you
c) same with grass , and sometimes with terrain and obstacles like rocks.