This question may be hard to describe, so I'll try my best to word it simply:

 

 

 

As you all know, after you stay in a specific area for about 8-12 minutes, previously aggressive monsters will no longer be aggressive. My question is, is the area of non-aggression relative to where you're standing after they become non-aggressive? Or are there dedicated areas of the map, where if you cross the imaginary line, they become aggressive again? I'll try to describe this with pictures:

 

 

 

Are the areas of non-aggression relative to the map? Where no matter where you are in the area, they still become aggressive after you cross the line? The white dots represent your character, and the white lines represent the boundary lines:

 

 

 

 

 

 

Or, are the boundaries relative to your position? Where the boundary lines form around your character at the point where the monsters become non-aggressive, like so? Again, the white dot represents your character, and where you cross the white line, monsters become aggressive again:

 

 

 

 

 

 

Knowing this will help me tremendously in slayer where I'm fighting higher level monsters.

I believe it's the first option, because the monsters move and you move, yet they will still be unnagressive if you move. Also if you think of the imaginary mage line, where they don't cross, but move backwards to lure you. That's my thoughts, if they make sense...

I believe it is outside of the range that the monsters are able to move, but I am unsure if all of the monsters in an area have the same range or not.

I can see how that would make sense, but seeing as each monster has it's own boundary it can't be quite right.

I don't exactly know, but I can say this. Say I walk into a room and start fighting monsters, and then after they become non-aggressive, I run to the other end of the room. If the room is large enough, I will start being attacked again. However, if when I first enter I first run to the other end of the room, I will have a different area of non-aggression, usually consuming the whole room. This can be observed at skeletal wyverns. I'm not exactly sure what to make of this, but there you are.