Here are a few ideas about the direction off map calls can take.
A
 Turn it into a channeling spell requiring direct LOS for the duration of the count down and perhaps the strike itself. This would make it so that scouting and countering is actually possible and would greatly reward forward, aggressive recce play. Counter battery could actually be a thing. Morale damage, movement or death results in the call being denied or at the very least the call being a lot less powerful.

B
Make the count down and AOE explicit for all players by visual warning like transparent red smoke flares coming down with an increasing volume that denotes the type of fire incoming.
C
Change the general design to strikes more about suppression and AOD rather than pure destruction. I picture early game calls being for smoke rounds or WP/Incendiary to make units run or render a position temporarily useless ergo reinforcing dynamic play. Mid game calls could be about a duration of low damage for area denial, like an attempt to walk 155 fire onto a specific point. A unit could be microed away from the artillery that attempts to walk into the bullseye. Good against static targets, good AOD to make a common corner or sight line inaccessible. Late game calls should be about making the enemy break position instead of completely breaking a position and the fun factor. Have artillery like the 380mm spool up damage slowly while having a high morale damage effect. Force units to run like hell well before max damage output happens.

D
Go the AoW super weapon route; Add a price to each call in so they will only work well in lower skill games or custom games where high point floating will be a common occurrence.

E
Tie type of call to the leadership mechanic. Gate accurate, high damage output calls to putting leader units at risk too.