Flares work, to some extent, but are limited in range, with a maximum of around 280meters. Consider a longer range option, either a larger flare that goes farther, or a ammo type for breech loading cannon.

For a larger flare, instead of using muzzle velocity, consider a range slider.

For cannon ammunition, because of the limitations of spawn range, a decent compromise might be to make them fly a set distance, say 1000M before bursting.

True military illumination artillery rounds had a maximum ranges of 8000-14000 meters, depending on the gun type.