I am not familiar with all the changes made since the very first version was published, but I'll try to address some of your questions.
When the AI is running the opponent or a player has assigned a mission to a large formation, (AI is running the formation) can all units of all types at all echelons including map bosses initiate a call for fire?
From what I understand a given line unit can call for a fire mission, where then the direct superior HQ will pass the call to organic artillery (bombardment) units. Such call may then be passed up say to a division's organic artillery unit, but also to the Corps' artillery assets (if available and if the unit is set to respond to such calls). The actual game mechanics might be slightly different, someone with more detailed knowledge may want to jump in.
I am reading on page 99, "When you order a force to attack, the HQ will often ... when the assault goes in and the assaulting units encounter the enemy, ...automatically call for the arty units to bombard the enemy...."
The meaning of "when the assault goes in" and "...encounter the enemy" is not readily evident when I play the game. So I also have these questions.
Are calls for fire restricted to targets which have at least one friendly unit observing? Can the Map Boss direct counter battery fires in general support of the many missions subordinates are assigned and executing on targets no friendly units are observing (?
In general, you need to establish visual contact, as aerial recon or sound detection is not rendered in the game. The term counterbattery fire refers to (an) arty piece(s) bombarding (an) enemy artillery piece(s), where the latter was (were) detected by aerial general recon missions, artillery observers on the ground or in the air (balloons or planes), by photometric detection (incident light/flash metering), or by sound detection (triangulation), where nowadays - in the main - radar devices and drones have taken over the detection role, aided by aerial recon to some extent. None of these are rendered in the game, so you need to have established visual contact once, at least. This means that no arty missions on enemy artillery will be carried out before at least one of your units has spotted such enemy unit.
I have seen friendly artillery units shelling enemy line units in woods for extended periods, even though the quality of the intel/position info had shifted from good to "poor", in prior installments of the CO series. That means that there was a high chanceof a friendly arty unit just performing terraforming, instead of actually harrassing an enemy unit, as the enemy unit had often long wussed out, due to the heavy shelling (either through routing or relocation).
Are in-direct fires only initiated when assaulting units are fired upon.
I am not sure here. I do think that it depends on the threat level, though, so it doesn't necessarily insist on actual enemy fire. In my books, a large enemy unit with heavy weapons, but outside the max range of any of its weapons, may still be seen as higher threat than an actual struggler unit consisting of 10 troops (with light weapons) right in front of (and firing at) your line unit.
Are calls for fire subject to communications failures? Jamming?
Radio failures are not rendered in the game (yet).
Except for the jamming of radio broadcasts (the Germans jammed BBC broadcasts), which was countered by the Brits by increasing the transmission power, by dropping leaflets (over Germany) which explained how to create more capable loop antennas, but also by adding more frequencies, the Germans did not use it to jam enemy comms on the battlefield.
In general, jamming was not used to jam military radio messages/communication. Even the radio communication between Russian partisans (behind German lines) and NKWD or Army HQs was not jammed, but rather used in attempts to triangulate their positions. There may have been rare cases where the Germans (and Allies, in 1944?) may have tried to jam particular military frequencies in particular narrow sectors, but - if true -, then such events can be seen as highly experimental missions. Since all armies had fully fledged messenger systems in place, the effectiveness of such complex and energy-hungry (usually stationary - at the time) device (that could not just be mounted on a single truck) was questionable.
After the war, East Germany (DDR or "GDR") maintained a number of large stationary jamming stations, meant to jam radios in and broadcasts from West Berlin, but also to jam the radios of their own citizens, so that they could not listen to independent news from places West of the iron curtain. The "German Voice" (a German radio station providing news and radio shows for the Eastern Bloc including Russia, but also for African and Arabian countries - including Iran) and AFN (i believe) could be received behind the iron curtain, despite East Germany's efforts. East Germany also operated various rather mobile devices and stations aiming to jam the first mobile phones in West Berlin and West Germany in the early 1980s, where some of the few users were known to East German services (politicians, director of the German secret service, other VIPs) etc. It seems like one of the main goals was here to find methods and develop devices to tap such phones, though.
Terrain and weather effects on radio comms? Phone or radio failure?
Not rendered.
Will a HQ executing a mission develop a fire support plan for the subordinate indirect fire units which would
* target threat locations from time assaulting units leave the FUP
* target threat locations from time assaulting units break concealment and now in threat units lines of sight
* target suspected or known enemy indirect fire unit locations?
* target retreating enemy units
* Sequence fires according to caliber and distance of assaulting units from objectives
* rolling barrages advancing safely with the advance of the assaulting units
A subordinated indirect fire unit will accept calls when the whole unit is on the attack, but also support other units (say sister units) when idle, unless you check the option where you limit support to the organic echelon (say a mortar coy would then only support its own Bn).
Afaik, indirect fire will not be laid on "poor" position intel. The intel has to be recent and has to have a certain quality.
Experienced players detach vital artillery assets and control them manually. It involves some micro-managing, but reduces the waste of ammo and the chance of useless "terraforming". Combining arty units to bombard units is also a very effective method, and it's also historical, as some nations performed that regularly.
Sequence fire is not rendered.
Rolling barrages are not rendered.
