It's strange because there are probably so many different theories and factors that determine future size. I mean you have genetics (sire/dam size), paw size, diet, also the "unexpected" size occurance (runt/largest pup), but never heard of the tail proposal. Funny thing is that when I got Badger, one of the first things I noticed was his tail length and size. I even asked the vet about how thick the base was at the time. I just thought that since he has a long tail that it took more muscle to hold it up LOL!! But the base of his tail is thick, not abnormally, but still pretty thick. So who knows? Also, when I questioned the vet about how they determine size, they said they take the weight at 3 months and times it by 3. If it is a large breed dog, they add about 10 pounds to the total. I've heard on this site that you take the weight at 4 months and times it by 2. So it proves that there are many theories out there I guess!!!