The encounter building rules are what I was going to post. I've never been lead astray by them. A lv +2 enemy is hard at level 2 and 20, though the lv 20 party of course has more tools and resources to overcome it, and the monster has more wrenches to throw into the monkeyworks.

I wish I liked the modules more. They're certainly well put together, but I just can't run stuff out of a box; I feel an obligation to tell the story instead of playing the game, like it was a movie or something.