So, I'm not sure I understand. I apologize if I am telling you stuff you already know, but I figured I'd just say it.
Unlike a shell from a firearm, a bolt drops from the instant it travels from your xbow. It never rises. Are you using a xbow scope? Every xbow scope I've ever used has a big X or dot at 20 yards. Then, it has smaller X's or dots at each 10 yard increment from there on (so a 30 yard dot, a 40 yard dot, a 50 yard dot, etc.). You will notice the space between them gets larger and larger (as the drop increases with distance).
So, if you are saying the bolt hits below your 20 yard dot when you are shooting 30 yards, that's the way it's supposed to be. You need to aim using the 30 yard dot.
If, however, you are saying your bolt hits below the 30 yard dot on a 30 yard shot but is POA on a 20 yard shot, then your scope is probably not adjusted for the speed of your bow. Most xbow scopes have a magnification adjuster. Once you zero it at 20 yards, you then adjust the magnification so you're spot on at 30yards. At that point, you should be spot on at further distances as well.
In other words, the scope is just "guessing" at how much drop you'll have. The actual drop will depend on the speed. So, you have to adjust the magnification of the scope to get the dots to line up to POA at distances further than 20 yards. Zero in as you normally would with a rifle (using the windage and elevation adjustments) at 20 yards....then, only adjust magnification to get zero'd at 30 years, then all of your dots should be good.
In terms of how far to shoot, that's really personal choice. I practice out to 50 yards routinely. In the field, I would probably never take a shot at an animal above 40 yards. First, they do have time to react to the sound the further you go out. Also, my groups get bigger the further I go out. Also, in the real world, I don't shoot as well as I do from my back yard with a nice rest.
If I misunderstood your question, please reply.
Last edited by 3D5DNJHunter; 07-11-2017 at 03:09 PM.