Indirect fire weapons always unavailable after firing?

[JacquesDeLalaing]

I wonder if I missed something in the manual. In the three scenarios I've been playing so far, it seems as if my artillery assets are almost always unavailable after they've fired, despite "arty ammo" being very high (90+). Which really makes me wonder if there is some hidden rule?

Follow up questions:
a) Does artillery also get to test on HQs before they test on "arty ammo"?
b) Do mortars use "arty ammo" or "ammo" for their tests?
c) I know that fire on unspotted hexes may scatter. But it seems that my mortars (Mission "The Gauntlet") scattered a lot even when targeting spotted hexes. Couldn' find anythin on that in the manual...

[Crossroads]

(a) Artillery only tests on base Arty Supply.
(b) Mortars are in arty category as well.
(c) Maybe there was scenario specific Lua settings for this? I’ll let Jason answer this one…