Nah the short one is the one that handles the obstructions constantly to go around buildings. The long range plans using bigger zones. When AI attacks I think two things happens. First the planning of the AI is done on the same thread as the rest, and thus slows everything, adds that the way the AIs handle units make them collide with each other a lot and that triggers the lag, because each unit is computing its own path taking into account all the other units around it.