I always watch sweat patterns. I can also say that I have seen plenty of horses, including my own, that when working on correct work will sweat back to front. These patterns carry through to the pasture when the horse is being worked regularly and the hind end is used to working fluently and carrying the weight. Even with no rider, the horse sweat primarily on its back, flank, abdominal, and hind end, I have one pony that will come in almost completely dry in front and drenched everywhere else.
When the horse is out of work for a while, or with a different rider, the sweat patterns will start to fall forward again as the horse is using the front end more.