With any HST method, the goal is to end up with a square with a seam along its diagonal. It should look like this:
After you stitch your HST to other block components, the 1/4 " seams will visually "trim" your HST on two sides so that the the points of the HST have moved towards the center of the block. This drawing has gray lines showing where the seam lines are on two sides of the HST.
Once you have joined your block to either other blocks, sashing and/or borders, the other two sides will be "trimmed" by the seams and you should have the seam running exactly from one corner to the other. (So, it should look like the first image, above, just 1/2" smaller in width and height.)