This is a very elegant solution and also consider the following: the less HP the PCs have to beat, the faster combat will end.
That said, you can consider the following scenerios:
- As said above, the death of key monsters may force others to flee or surrender. Use it at your discretion
- When more than half of the enemies are bloodied, they may also flee or surrender. Same discretion
- When dealing with single beefy enemy, you can make a rule where the enemy suffers double damage after bloodied, or before bloodied, or just tweak the enemy's total HP. Either way, give it an "action point" when it reaches bloodied status (or at your discretion) to make up for the loss of beefiness!