What is the distribution of looks? It's very high-schooly to jump up with the answer "normal distribution." Why? Because we're not dealing with a small, fairly uniform group of mid-teens girls.
Worse still, the college scene, the club scene, where chatter about rating is more likely to be heard, is full of men who are too young for marriage, with similar-aged women -- that is, women who are too old for marriage. Within that environment, few men are going to arrive at the conclusion that 14-year-old girls are the best bride material. This most-important point never gets noticed while they make a fuss over silliness about dragon tattoos or brand of purse, as if they were Chinamen rattling on about the size of hands and feet.
On the one hand, looks deteriorate with age. Women hit their peak about two to four years after menarche, and then decline at a consistent rate. Constant decline = linear.
On the other hand, for any one particular age, looks will be distributed normally. What does this do to our line of looks vs. age? Turns it into a scatter diagram without having any effect on the central tendency. (Except that the variation also decreases with age: there's hardly any difference between the most-beautiful 99-year-old and the most-ugly.)
So, when we start summing up total numbers of HB 7s, HB6s, and so on, we find a simple second-order curve that is the definite integral of the line of looks declining with age.
Just to make it easy sleazy, do what I did, and use a simple multiple such as 3/2 to describe the greater numbers of HB (X-1) compared to HB (X).
That's why I say that only 1 out of 9 women are HB 5 or better. Anything above HB 5 and, odds are, you're fooling yourself by rating her by dragon tattoos and brand of purse.
