RE: Why do I consistently SUCK at sharpening 3 blade heads?
 

I use G-5 Montecs with my crossbow, and Snuffers with my trad bows. A good diamond stone and the instructions that G-5 offers on their site is a good way to start. http://g5outdoors.com/#sec_video
I find a few strokes point-first down the diamond stone finishes the edge nicely.
BTW - the Snuffer is much easier to sharpen and takes a better edge than the Montec.