Yeah, and it’s also just a matter of breed, too. Some tails just naturally stay up. For example: is this dog always dominant?
Well, he might be for all we know, but his tail base also just naturally stays high. It’s really not smart to use just one behavior as your sole determination for something like dominance.
…Which again, is a relationship between two animals, not a character trait. You can’t look at this dog standing alone in the park with his tail up and say “Ah yes, he is the most dominant. Of all the dogs. Which is just himself.”