I've got a Sportdog 1825. This unit is rated for 2 miles. As a matter of fact, the vendor says this is one of the longest range units they sell. Anyway, a setting that generates a yelp from the dog at close range seems to hardly get a response if the dog is 50 or 60 yards away. So what I'm seeing is that it seems that the further the dog is away, the less of a shock he's receiving. Anyone else notice this with their units?