I find that if you are careful in the preparations those patches go together easily. It's when we try to go fast or cut corners that we get into trouble. I like the idea of pressing the square on the diagonal to get it accurate. Then if you draw a scant 1/4 inch line on each side of that crease and sew on the line you draw, the half square triangles come out correct.
Patience and preparation is the key. :)
Connie