Wrong, wrong, wrong. The only variable is the arrow. Yes shorter arrows will decelerate faster but it doesn't matter what gets them going that fast. I will say once more.....shoot the exact same arrow (weight, length, fletch) out of a crossbow and a compound bow at the same speed and they will have identical trajectories. Crap, if you could throw the arrow or shoot it out of a cannon at the same speed it would have the same trajectory. Yes, a crossbow arrow has a different trajectory than an arrow shot out of a compound bow but that's only because the arrows are different. The arrow is the variable, not the means of propulsion. This is Grade 9 physics sharpstick. Not trying to be a dick here but this is pretty simple stuff.

Your post above was 100% on the money until you added that last sentence.