S1eth said:
flat_chest breasts large_breasts
[0, 1/3] (1/3, 1) ~1In my opinion, both tags should be used if the image is borderline and you can't tell for sure if the breasts are smaller or larger than 1/3 of the head. The only other option would be "guessing".
Personally, I would support estimating like that. Part of the reason we use this kind of metric is because it is generalized enough to (ostensibly) prevent too much confusion or bickering. I suppose someone could use 3D rendering software to get a more accurate reading of volume where head size vs. breast size is concerned, but that just says the user is being too uptight about it to me.