I know of no set distances for throwing hawks. That would be almost impossible unless you also mandates certain length and weight restrictions on the hawks. I have never bothered to use a tape measure when throwing, but if you are going to throw the hawk underhanded, blade forward, you do need to shorten the distance some from what you use throwing overhand, blade forward. It probably will be about 12 feet, as has been suggested.
Welchman: I am trying to make heads and tails of your post. I don't know what taking " 5 steps and another back " means. Does that mean you take 6 steps back from the target to throw overhand, or only 4 steps? I don't know how long your " step " is either, so this doesn't tell me any useful information on where to stand to hit the target.
When we are throwing overhand, we are 15-16 feet back of the target. Where each man stands depends on his height, his arm length, the weight and length of the handle on his hawk, and even where he grips the handle. Since we each step into the throw differently, even the length of our legs, and how long we stride affects where we begin when we throw that hawk. I remember having to find a spot that was comfortable for me, and even that changed as I got more experience, and relaxed more.