You need to know what your goal with a drop hanging is. It's assumed that a (calculated) long drop hanging will provide enough force to the neck that the cervical spine will break, effectively resulting in an almost instant death. The length of drop, body weight and type of ligature used are all (extremely) important considerations in a long drop type of hanging, because too short a drop will only inflict more pain than necessary, and too long a drop can partly or fully decapitate the body, making it more gruesome than necessary.
When it comes to suicide, I can't think of any reason for decapitation being considered a failure. If you go for a long drop, you would then just set the drop to an extreme and use a ligature that is thin, strong and has low stretch. If breaking the neck or decapitating your body is not your goal, what would be the benefits of having a drop? In partial or full suspension, your body weight should be heavy enough to close a ligature that is not too unwisely chosen, and essentially strangulate you.