It was just like the ancient strategic passes, where there were millions of troops, but only a few dozen or a hundred enemies at a time.
However, there was also a great risk in fully contracting. When all the forces were concentrated around the new middle route Island, once the enemy penetrated the defense line, they would not have any redundancy, and they would directly face the desperate situation of the Stargate being destroyed and the entire Army being wiped out!
On the contrary, although the expansion of the flexible defense line was fragile, it was like layers of film. The defeated Army could regroup at the defense line behind them. Whether they chose to integrate into the defense on the spot or continue to retreat, it would give the main camp enough time to react.
Even if the battle was beyond redemption, they could still recall some of the seed teams through the Stargate, so that they would not be completely annihilated!