As a designer, I don’t like to create new things. Yes, that’s right. After you tell enough lies to get your game going, any further lies you have to tell should be in the context of what has come before. You think you need a new mechanism? New pieces? Consider trying to address the problem you see in terms of what you’ve already created. Be careful you are not creating more problems or opening more doors than you intend. Everything that rises must converge.
So much for design aesthetics. On to artillery. In the context of one-off scenarios the basic rules are okay. Lines of sight across perfectly flat terrain without depressions are easily had most of the time. But this is a rare case on my maps of Lower Normandy. Indeed, spotting for artillery was a real challenge historically. Using the base rules on playtest maps often resulted in artillery being used as a turn-ending throwaway called at very close range to friendly forces. Sure this sort of mission was fired in 1944 but it was still with great care and rarely in haste.
The US Army considered that danger close, the closest distance to friendly forces that a mission might fire was 500 yards, or 12 hexes. Absent very large maps, artillery is difficult to portray in games with 40-yard hexes. Even 32×24-inch map would need to have four map sheets before you could reliably work observation posts into play. Infantry battles throughout the Western Front in WW2 can be understood as battalion operations with the objective of securing observation posts for their, and their regiment’s, next maneuver.