The rule sounds good and may allow for further breakdown say by unit types or by country - say US infantry Coy commander may call in artillery (albeit limited - say only "his Bn" mortars, only onboard or only one bty of offboard. Russian inf. coy commander may only command mortars directly attached to his company. Or to neighboring coys... Actually pretty interesting topic. Lets brainstorm
So... for example:
1) artillery/mortars assigned to "hq company" (ie subordinates of A0) may be called in only by units with FO authorities. Alternatively, "proper" artillery just by FO's, mortars also bz co. commanders.
2) Mortars (50-82mm) and inf guns may be attached to individual companies. Depending on army comm situation, only the given Co. commander or (if comms are better) also commanders of neighboring Coys may call them in.
3) Mortars directly attached to Coys are inaccessible for FO's, but accessible for A0.
4) in better comm armies (now that's more in the MBT era) the authority over arty may shift one level down, so for example in Fulda Gap 1980, Plt. leader may call in company mortars and coy leader may call in offboard arty.
5) (again modern) GPS-equipped FO's can call in arty at two targets at once (maybe only if calling in "modern" guns? IE if you say buy GPS FO and Allied/Captured ZIS-3 76mm battery, you cannot, if it is a MSTA-B battery, you can?)
What think ye about such an amendment?