Help-when-attacked distance

I have modified combat acquisition range of enemy units to something rather low, yet, when I attack an enemy unit, it's friends come to help from rather far. I have no idea where to look for something that modifies this; under gameplay constants, in the object editor, perhaps it has something to do with AI...? If multiple solutions are possible, I would like one that allows one of my opponents to have longer "call for help" distances than the other (the two players use completely different unit sets, so if the solution is unit-specific, that's ok too).

Right, almost forgot, it's a single player map, both computer players have no special AIs (they just stand there and wait for you like creeps do, except for some units that will be ordered at map initialization to patrol around, and some scripted events).

If the enemy units are neutral hostile, then you'll want to change the gameplay constants field called "Neutral hostile- creep call for help range". It MAY also work if the units are computer-controlled, but I've never messed with it.