• We have updated our Community Code of Conduct. Please read through the new rules for the forum that are an integral part of Paradox Interactive’s User Agreement.
Yeah and they talk about a "ballistic system"...
8ZZeg7Q.png

not all artillery is off-map. Also the Gameplay screen shows (probably) that for that offmap artillery you need another unit to call it in.
 
You surely need a forward air controller or forward observer to call in OFFMAP stuff. But i think there is also on map artillery available to Hummel or similar like 155mm. Stuff above is probably offmap.