Jenn, the Flock block is a 4 patch. If you were going to make it in 9 inch size, then each of the larger half square triangles would finish at 4-1/2 inches. To make those, you could cut 5-1/2 inch squares, make the half square triangle, and trim it down to 5 inches.
When you get to the smaller triangle squares, they would finish at 2-1/4 inches. So you would cut 3-1/4 inch squares, make the half square triangle, and trim down to 2-3/4 inches.
The reason the 6 inch block works for many blocks is that is is a multiple of 2 and of 3, so it's easier to make 4 patch and 9 patch blocks. The 9 inch size block is doable in this block pattern, but as you can see, figuring the numbers gets a little messy. You might want to pick some other 9 patch blocks if you want to stick with 9 inch finished blocks.
Happy Quilting,
Kathy