Realistic boobs size

So in Pony2.2 there is the lora called "Breast size slider". I wanted to use it to get some realisticly medium sized boobs. When I enter -5 it gets automatically corrected to +5 ( see image 2 ). Even when I enter 0.1 the boobs are still extremely large. Is there a way to get more realistic looking A and B and C cup boobs? Why do they all have to be G, F, H and larger? I understand that it is to prevent making images that look underage, but grown up woman also can have small or medium tits.