[4e] Houserule Suggestion

[JaxGaret]

The first is, half hit points is half the danger

Incorrect. Two monsters at half hit points each are stronger combined than the same monster with normal HP by itself. Why? Because they are dealing twice the damage per round before one of them drops and pose twice the number of targets/flanking partners, that's why. Also, economy of actions matters: it's always better to have more actions than fewer actions, all other factors being equal.

Just try it. You'll see that it works pretty well. If you reduced their HP by 25% instead of half, you will have monsters who are quite a bit overpowered.