Lamy Fountain Pen Nib Confusion???

A while back I was sent a Lamy Safari in Pink as I had been wanting one for so long, I was a bit down at the time and one of my Twitter friends said they would send me theirs as they didn't use it. It was amazing when it arrived, it came with a pink Moleskine notebook and some pink ink, which was more purple, but still adorable!

I loved the pen so much, but then one day I noticed the Nib said F (Fine) so I decided to test it against my M (Medium) Blue Lamy Safari, which I had bought a few months prior to receiving my Pink Safari, which I love.

You can just about see the M, but you cannot really see the F

Pink = F
Blue = M

I did a little writing test with the Lamy's below...

There is hardly any difference, not enough for it to be noticeable when I am writing normally.

Has anyone else had this issue??

Is the Extra Fine noticeably finer??