Setting TRIGGER_MASSIVE_ENEMY_COUNTERATTACK_AT_DRASSEN to FALSE only disables the counter attack for Drassen. You'd also need to set AGGRESSIVE_STRATEGIC_AI to 0 in order to disable counter attacks on other cities. What you experience is probably just a regular group that comes looking after liberating a city. Counter attacks are 4 groups of <CounterAttackGroupSize> from DifficultySettings.xml. As they usually travel in a pack you'd see a big group approaching the city and they would coordinate the attack to arrive simultaneously. At least that's what they always did in my games.