i am starting to think that the hex dices may actually not be completely random as it has a top and bottom so it may depend a lot on the way you throw the dice. you may favor one side more than the other!
maybe using a regular dice is better, they are easier to come by too.
or maybe using a Teetotum with 16 sides (although i have never seen one with 16 sides). here is a picture of one with 12: