This is a problem with any fixed-point sight (i.e.--crosshairs, pins,red dots). It's the old high-school physics problem,"If a squirrel was sitting x-feet up a tree,was looking at a gun's muzzle, and a hunter X-yards away shot a projectile moving at x-feet-per-second, would the squirrel be struck?" When I first went archery hunting several decades ago, I was taught to aimlower on the target otherwise I'd overshoot the animal. Knowing the range of the animal from me allowed me to pick a pin, but I still had to pick a lower point of aim than where I wanted the arrow to hit. The whole issue was nullified when I started to use a pendulum sight on a vertical bow. After being sighted in, the swinging sight compensated for the trajectory and distance. At a certain distance all bows will have this same problem. Having just starting to hunt with a scoped-crossbow last year, I had to remember the old rule. Unfortunately, the only way to know if you must aim lower, and how far, is to practice with the bow, and then remember to adjust appropriately when hunting. Incidentally, for a given mass of projectile there is a velocity at which height and distant are irrelevant. This is why you don't have to have a different point-of-aim with most guns fgrom an elevated stand. Since I haven't seen a pendulum sight made for a crossbow, practice at varying heights and distances is key. In your case aiming at a 17-yard target with a 20-yard pin from an elevated position put the bolt's point-of-impact too high. Converesely. aiming with a 10- yard pin at a 17-yard target {which would be the same as aiming low with the 20-yard pin} produced a kill. File that in your memory bank and practice and experiment some more. It's obvious that whomever said all you gotta do is point a sight and shoot did not spend much time target-shooting and hopefully isnot hunting either. Sorry for being so wordy, but sometimes I must remind myself of the basics no matter how sophisticated the equipment becomes.