Instead I provide an opinion and one I support from another authoritative source, Linda Shaw:
"I have no idea where the idea for thoracic spires rising higher than the top of the scapula came from, except maybe the horse world. I know of no big predators that show this. Predators have much more flexibility of the forehand than horses, cattle, deer, etc. Cats have the most. They can spread their front legs wide apart almost like a human, the better to grab a big prey animal. Canines have much less ability to spread their front legs, but more than prey animals. Dogs and cats can both drop their chests down to ground level and still crawl, sliding the chest down between the shoulders. Then you see the scapulas really pop up. They can rotate the scapula to an almost level position when they are galloping and thrusting the front legs out almost level in front of them. The scapula can rotate the other way, to totally upright, so the front legs can drive way back between the back legs. Horses cannot do this. Their scapulas are strapped to the chest wall with more limited ability to rotate. They need tighter shoulders that can support their great weight. Elephants have upright scapulas that have almost no ability to rotate. They cannot trot or gallop, only do a running walk.
It is easier to feel in American show dogs with soft, loose shoulders. You can get your thumb right down between the scapulas and feel the thoracic spires. In working lines dogs, especially fit ones, all you feel is hard muscle. Maybe in some really roached dogs the spires could be palpable above the top edge of the scapula?
In my book I included a couple of anatomical cross sections, that show at no point do the tops of the scapulas drop below the tips of the Thoracic spires, when a dog is standing normally. "