I would agree that knowing the parameters of your setup would be key in choosing what mechanical (or any head for that matter) you were going to use.

Angles can be tricky. I can still be occasionally fooled on the severity of an animal's angle after many years experience. Additionally, unexpected things can happen under field conditions.

For example shooting 70 pounds of kinetic energy coming out of a well tuned bow, should be more than enough to put a two blade broad head completely through any deer standing broadside, if no bone is hit, right? Well, I thought so too, until I failed to get a complete passthrough on a rutting buck one time, although he still went down within eyesight.

I have seen the same set up put a two inch cut three blade mechanical completely through a number of nice bucks.In fact as I recall, the only time I didn't get a complete passthrough with the three blade two inch cut, the buck ran off with most of the arrow sticking out of his side. I had a sickening feeling when it happened because from my perch thirty yards away it appeared like there was minimal penetration into the rib cage as the buck ran out of sight. When I finally got down and checked the bloodtrail a blind man could have followed it. The arrow penetrated perhaps 12 inches or so and was still stickng out of the deer when I found him about 100 yards later. Upon dressing out the buck it showed the shot only took out one lung. You could have knocked me over with a feather.

I guess what I am trying to say is, even when conditions are perceived as ideal, there still can be some surprises. In answer to your question, I would never use any head that I wasn't 100 percent sure would do the job on a quartering away animal.