If you make a generic 2" half square triangle, you can make a block anywhere from 2" to 20", you just need more patches for the larger blocks. The Qubes have a set of generic pieces . If you look at the individual listings for the Qubes on the Accuquilt site, the specific sizes of the patches are listed.
https://www.accuquilt.com/go-qube-mi...-12-block.html
So a 12" Qube has a 6" finished HST, so 4 would make a 12 inch block.
the 8" Qube comes with a 4" HST, so 9 (three rows of 3) would make a 12 inch block.
The dies are generic shapes that work together to make the blocks shown on the side of the box and the result will be the exact size of that Qube. Since the dies are generic shapes, however, you can use them to make different blocks not listed. More of the smaller units can be put together to make larger blocks.
I'm guessing that Eleanor Burns was demonstrating a 12" block that was made up of smaller patches, so she used the 8" die. Hope this makes sense...