OK, so here's a good example of a place where not only us, but everyone - from the Demo Team to MegaMek to the game's writers - are playing the rules wrong because they take too long.
For anyone who wants to follow along, the rules references are TW, p173, TacOps, p184, and BMM p77.
When a Building is struck by an AoE attack (including Bombs, Artillery, and Artillery Cannons), follow the following procedure:
1) Triple the standard damage in the target hex.
2) Double the standard damage in the 6 surrounding hexes.
2) Double the standard damage in the building level above and below the point where the AE damage hit.
3) Apply the standard damage again two building levels above and below the point where the AE damage hit.
4) AE weapons deal double damage vs buildings (p174) - note that whether this doubling is additive or multiplicative is left unsaid
In practice, this would mean that, at a minimum and assuming additive doubling, an indirect Long Tom shell which hits the center hex of a 7-hex area building, would deal the following damage:
Center hex: 60 points (double damage v buildings) + 90 (triple damage as p173) + 60 damage (double damage against 1 level down from the impact point) + 30 damage (standard damage 2 levels down from the impact point) + 0 (no building exists above the impact level). Total: 240 CF per hex
Each adjacent hex: 40 points (double damage v buildings) + 40 points (Double damage in 6 surrounding hexes as per p173) + 40 (double damage against 1 level down from the impact point) + 20 damage (standard damage 2 levels down from the impact point) + 0 (no building exists above the impact level). Total: 160 CF per hex
Note that, since many attacks only partially damage buildings (due to the building not being in the AoE), this has to be calculated, by hand, every time an artillery shell splashes a building. Given the limited hours we have to play, and the fact that you guys like to have artillery available, this is simply not a tenable rule for use in our group.
For the duration of this campaign, unless a particularly solid reason comes up, we will continue simply doubling the damage when a building takes CF damage from an AE source. That is a reasonable middle ground between the insanity of the TW ruleset, and the BMM BSP rules, wherein artillery does only its base damage to buildings and isn't increased whatsoever.