SPOILER WARNING FOR GRAND CAMPAIGN
Thanks, Luke! My group just played our first session and we discussed how to apply the +2 to hit before we started playing, and decided to use the same approach that you outlined in your response. The four PC party brought some of the former thralls into the dungeon at location 29.08 and they absolutely destroyed the purple worm in like three combat rounds because each attacker had a +18 to hit in the first round and they took away over half the worm's HP immediately. I was reflecting after the session and I figured we must have misunderstood the intent of the rule. A to-hit bonus of that magnitude made the combat seem like a forgone conclusion, but I suppose that's the benefit of bringing a large party to concentrate force on a single target. The worm did eat four of the former thralls though! Love the game, and I'll probably have more questions.