Imagine you're in Sunhold. The Moarmer, a hostile military is taking the City. They're in the streets, hunting everything down. It's a War zone. You turn the corner. There's six of them plus their summoned war beasts. You and their group are in direct line of sight. Some may even have their eyes pointing in your direction. All logic dictates they should have seen you emerge from that corner. But they don't do anything. They just stand there idle, like you're not even there. Cause their aggro range is shorter than where you are.

Detection and Aggro should work based on line of sight, no matter the distance. Especially in instances like Dungeons. If your character model is within unobstructed line of sight to a hostile mob, that mob should notice you and become aggressive and charge. This can change several things.

1. Encounters will give you less time to prepare for battle. Being careless (or overconfident) in a hostile situation could be punishing.
2. Using the environment will become even more important for Stealth play and remaining undetected while not sneaking.
3. An increase in Immersion is always a plus.