To some extent I guess. People like Cesar Canas and Dani Comas are over 6ft with long legs and arms which in comp situations helps with strato dabs and they are also quite springy. However, Marc Caisso is of a similar technical level but is probably only 5'6". Weight again is not a constant. Muscle weighs more than fat and so provided the rider in question is lean and isn't carrying any extra weight it shouldn't be an issue.