Not all 400 yard marks are the same. Some stand out and are clearly viewable, some can't be seen at all. In training we often throw a bird a few times before attempting a dog, too test visibility. I want to get the most out of it for the dog and be fair to them. While distance is important, I want to train to success and sometimes conditions just don't allow for distance. I'd rather do 200 yards and get something out of it vs 400 and get nothing