Barrel length, bore, porting and even material it's made of will affect the flight of your paint. By how much is debatable, especially after you factor in the inconsistency of most non tourney-grade paint. Either way, you adjust the velocity to suit the equipment/paint you're using. If u find your new 16" barrel has reduced your range, increase the velocity a touch.
You have an Impulse, right? You can increase the velocity either by the vertical regulator, or by increasing the dwell. Do it in TINY increments though, because the ball-to-bore fit is much more likely to affect velocity than just the length...
Does that help?