How do you actually separate size from sharpness?

I’ve just watched the transvoicelessons video about sharpness and dullness and I do understand that they are not the same thing. When changing from sharp to dull, and dull to sharp, my size changes. In the video it says that one way you can separate the two is to try and change it at a larger size but when I become sharper I get a more feminine size.

I don’t understand how you can change sharpness by altering the position of your tongue and also not change the size of your size. I must be misunderstanding something.