Flexbox make one item 4x bigger than other items

I am looking at this Flexbox cheat sheet:

http://www.sketchingwithcss.com/samplechapter/cheatsheet.html#wrapcolumn

Here we have an example:

I want to make the bigitem 4x bigger than the smallitem, not 2x as big, but I cannot figure out how to do that?! I tried substituting 4 for 2 and no that didn't work.