I think a bit more - I'm 10 stone and I ride and jump 13.2hh occasionally. I suppose it's not regularly but he feels as easy with my weight as the 16hh.
Our 14.2hh Connemara used to go XC with 12stone up --the jockey coming back complaining about how hard he pulled. He is very powerfully built with very big muscular hind end and strong neck. I have read approx 20% body weight of horse.
Connemara weighs 430kg on tape so could carry 86kg approx 13stone.
It does relate to build of horse and fitness as well
If you were watching Olympia--comments about previous jockey of Edwina Alexanders horse they reckoned he was around 16stone on 15.2hh not exactly built like a tank.