...can't some of the goblins call for help or something.
I think that's what the war drums are here for, the enemies try to use them if any are nearby.
It also doesn't help the story and immersion that Minthara is on the other side of the wall and you're on the rafters throwing out spells and yelling verbal components and hearing Goblin death screams.
In my opinion it is fine as it is, but I can understand that it's a bit ridiculous how NPC's won't notice some things.
There is the problem with balancing too. If the range where this is noticed would be increased, many places will be much harder as the levels are probably designed with the current range in mind.
Such things are a bit hard for developers, because there will be always a group of people who won't be satisfied with how things are or will be. (I wouldn't want to be in their position.)
In my opinion changes on this part aren't that important and I wouldn't have a problem with it, if it stays as it is.