Reviewing from many sources about WWI, I just thought that long range weapons in this game (Artys, Railguns, Cruisers and Battleships) are truly overpowered, with the ability of decimating entire armies with much ease and without compromising other units in the fight (infantry, cavalry, tanks, etc.)
Although I recognize artilleries and other long range weapons were truly essential in that war, I found, in some way, unrealistic that fights can be decided by player's ability to build and use as many artys as possible and to neutralize enemy's artys. Since most of the battles fought in World War I were mainly combats between soldiers and tanks AFTER artilleries and other long range units barrage, my idea is to handicap those units' damage against those short range units.
In other words, while long range units still would have the power to destroy enemy units, they'll lose effectiveness progressively as those units are reduced from army groups to armies and corps, whatever the number of long range units used in those attacks, until being useless against divisions and brigades, since such low quantity of men can protect themselves against that fire power, hence compelling the player to use short range units to destroy the enemy force.
Of course, other features of those long range units (damage against air force or buildings) will remain unaltered.