The cutoff is and always will be ~3.41% (it's the value such that the odds of going 20 battles without seeing that Pokemon is 50%). This information has been posted in a great many places, which is why I deleted your post.
so, would you be willing to offer it? If you don't wanna spend time breeding it, i can also clone it! Also, judging by your join date it seems you either lurked for a while before joining or are somewhat of a newbie.