Spotters are not, by default, Forward Observers. They are, merely, another team member for the weapon. They serve no other purpose, at this time.
I believe that Cannons are Direct Fire weapons, as they are listed (
In Section 19 - Weapons and Equipment, p.120) in Subsection
21.4 - Heavy Guns (p. 133). They are not listed in Subsection
21.5 - Launched Weapons, which are, by definition, Indirect Fire weapons.
As a fluff note, the Unholy Carronade is described as firing a "bolt of Symmetry." I know of no bolts that follow arching paths to their targets.
Arashis are designed for the caverns of Mercury; can't be a lot of overhead open space for indirect fire, there.
