I realize I posted this some time back, but did you ever get a chance to look into this? The reason I ask is because I still seem to be noticing some anomolies with the spawn rate. It doesn't seem to happen every time, but occasionally, upon killing a monster, it will respawn immediately. I've noticed this at both shame and the cemetary near cove. Also, my brother was in wind and witnessed a demon get guard whacked; it then respawned just out of the guard zone, came towards him to attack, and was killed by the guard again. It once again respawned, but further out.
My Mage often uses blade spirits, could this, perhaps, be why? This might relate to the guards in wind, as perhaps the engine respawns creatures it sees as being killed by NPCs.
Just some observations. Let me k ow what you find.