I've always seen snowball blocks with the triangles in the upper one-third corner, so the finished size of the triangle is 1/3 of the size of the block.
So, for example, if you have a 6" snowball block, the finished size of the triangle is 2". Be sure to add the seam allowance. If I remember right, this translates to using a 2 3/4" square on the corner.
And if you sew along the seam line for the snowball block and a second time 1/2" closer to the corner, you end up with a bunch of bonus half-square triangle squares.