Have you ever tried using triangle paper? I love it and use it 100% of the time when making half square triangles. They are always perfect. You can buy it in any quilt shop based on the finished size needed. Also, I found a web site where you can print it out at home, it is blockcentral.com. The problem with printing at home is that the paper used in the printer is thicker (even if you buy the thinnest cheapest stuff) than what the purchased triangle papers are. I invested in one package of every size and have not had to repurchase any but the 2" in over 4 years.
Mindy