My personal experience is, the weight is the big factor. Also, much practice. I typically maintain a distace of twelve to fifteen feet for shuriken. Shaken can go a little further, 20 feet to 25 feet. Knives I can throw with one rotation, occasionally a half rotation, up to 40 feet. At 40 feet, my lighter knives will usually veer off target, after a number of throws, I can correct this, for the most part. I usually use an underhand throw for knives, I personally find this to be more accurate. Side throws for shaken tend to veer off course over long distance, overhand throws tend to stay true, just more difficult to account for a drop in height. Optimal range, I would say is up to 12 feet for all.