Ever seen a big female sativa, 12' high or more? I don't think size is an indicator of sex. It's just genetics.
Just because its a tall growing strain does not mean that the males are not going to be taller than females.Get what I'm saying.
Have grown out well over 200 of a particular seed batch under identical conditions and still would not feel confidant to go by height/growth rate to predict sex.
supposedly this is ED R.'s Theory