I'm trying to convert The Forgotten Forge from the back of the Eberron book into 5th Edition to run it, and right now I'm trying to get the enemies inside it converted over, using the UA article as a guide in some places. However, a big sticking point I'm finding is getting the enemies properly converted into 5e's rules. I've found a few guides (like 3.5 to 5E simple conversion guidelines) but all of their methods for converting hit points leaves the monster with far too few hit points as far as I'm concerned.
For example, a CR 2 creature from the adventure (the Warforged Rogue on pg. 312, if anyone has the book) got converted over with only 18 hit points, and all the guides I'm finding seem to say that's correct. However all other CR 2 creatures I've looked at in 5e books have far more hit points, and CR 1 creatures tend to have more hit points than that. For comparison, the Goblin Boss, a CR 1 from the MM, has 21 hit points. Am I doing something wrong? Am I wrongly expecting the CR to convert over a little more directly?
To be clear, what I am asking for is a way to convert a CR 2 creature from 3E into a CR 2 creature from 5E. The DMG almost helps, but the hitpoints it lists seem too high.