The average breast size for women is said to be 36C, what percent of women that size can pass the pencil test?

In another thread discussing breast size and its possible relation or comparison to the male penis it was said that brasize.com had the US average at 36C, confirming what I had heard some years back. The next thought I had was what percent of those women who fall within the average could or can pass the pencil test? I would predict at least 50% but it may be higher, or sadly less.