I have some invisible minions who attack people, it's part of a spell effect. They use a weapon with a Ranged ability and NONE weapon proficiency. I hope to get the straight THAC0 this way. But, because they spawn next to those they attack, they endure -8 to their attack rolls. I compensated by giving them a +8 bonus, but along the way it began to seem that I don't quite understand attack roll messages. When I had tried giving the minions bastard swords to do melee attacks, and these characters had somewhat different AC (6, 8, 10), the attack rolls on them showed different bonuses.
See this fabulous screenshot:
All the while Edwin's AC was 10, Xan was second worst with 8 and Imoen had 6. The minions had no special advantages with swords and anyway they were identical. So why does the window show huge bonuses to their attack rolls - and not even corresponding to the relative AC values? Why do they get + 0 against Edwin with the worst AC and +4 against both Imoen and Xan, as though their AC is the same?