Properly understanding “small frame - medium frame –large frame” thing- I feel like I have the wrong idea about this

I know about how to figure out your frame size and everything but I’m just worried that I have the wrong idea about how frame sizes work. I thought that someone with a small frame would have small shoulders, a small head, etc., and a medium frame would have a medium head, medium shoulders, etc. and large frame would have larger shoulders or a bigger head (no offense to anybody), etc.

So, then I thought I was the only person with a medium frame at school because I didn’t see anyone else with a head as big as mine or hands or wrist, etc. However, it turns out, during a discussion with a friend who I always assumed was small framed, she has a medium frame as well and  her wrist is the exact same size as mine.  But she has small-ish shoulders, hands and head. I’m not sure if it’s just her.

Looking around, it seems a lot more girls are medium framed than I thought. But how can this be if apparently only about 20% of women actually have larger frames and most women have small frames?

Also, most of those girls who have “medium frames” seem to have small heads, hands, shoulders, etc. just like the “small framed” girls. So am I wrong in thinking that a larger frame means a bigger head, bigger hands, shoulders, etc.? Or does it mean that no matter your frame size, your head and everything else will be still be small but instead of being wider, your bones are just denser?

Anyways, most of these people are ectomorph so I wonder if that has something to do with it. But does being mesomorph mean that even if I had a small frame, my shoulders and head would look bigger than what’s supposed to be for my frame and so forth? 

(I'm a medium frame but I've been told I have a huge head and hands but don't know if that's actually the case because it was short people with dainty bones who told  me this, no offense to anybody-- maybe anything other than small heads like theirs are big in their opinion)

I’m not trying to sound ignorant or repeat the same question over and over about frame sizes- I just want to be sure that I didn’t get the wrong idea.