Protected areas need to vanish the moment reinforcements run out. Nobody likes to wait 6 minutes to finish up Spartanovka because there's some doofus with a scoped rifle busily defending a tiny portion of nowhere way in the back. The whole purpose of them is to deter spawn killing anyway, right? No more spawns, no more need.
If there was a protected area death achievement, I'd already have it. It's real easy to miss the silent warning when you're scanning for targets. It needs the same shouting and screen dim that going out of bounds does, and the areas themselves could bear to be trimmed down on a lot of maps. They're often huge and cover places that nobody spawns remotely close to, and often that are tactically important to the nearby capture zones. The courtyard behind the Univermag in Fallen Fighters comes to mind. Protected Area for no real reason at all, except to make it a major PITA to sweep the buildings overlooking the third park capture point.