Spent quite a bit of time figuring out how to do this. The key is to measure slightly from the side. Push gently into the pelvis and measure from pelvic to tip. Took some time deciding if this is a legit thing to do, but after some testing, decided that when I'm slamming the wife, she's getting the extra length hidden by that thin layer of fat there anyway (I'm don't have a lot of body fat).