When I have blocks that are not "exactly" the same size and I am putting them on point, I make the triangles larger than needed and then make the "new" blocks the same size. This corrects the irregular size of the original blocks and is not noticed unless measured. I make my triangles by making a square the size of the original block, in your case I would make the square 6" to cover all block sizes, then cut the square into two triangles. This method may not be the precise method used by advanced quilters, but it works for me. Good luck.