In the truck, Ren Xiaosu listened as the thugs of the Razor Sharp Company discussed their plans to break through the defensive line at Mt. Dingyuan. They not only had to think about how to break through at Mt. Dingyuan, but also consider the possibility of the enemy's reinforcements arriving from Mt. Guan.
The reason Mt. Dingyuan was difficult to capture was because the Zong Consortium's bandits were supporting them from the front line of Mt. Guan. In peacetime, the two groups of bandits looked wholly unrelated. But when war broke out, these two groups were clearly fighting on the same side.
So if they attacked Mt. Dingyuan, they would have to face the threat from Mt. Guan at the same time.