If you gave the helo's an "area" attack, in essence you are giving them a search and destroy mission. You designated the area and then its hands off. If the area you gave is void of enemies (or enemies the air assets can see) the air assets will end the mission.
You should be able to adjust the mission BEFORE the air assets arrive, but not after they show up. They are NOT artillery with a long enough duration to adjust. Point attacks will normally drop a bomb, Line attacks with use guns or rockets for helos....its not like you expect them to hit the same spot OVER AND OVER again....that the artillery's game.