General Felix certainly knows that he can hold on for five days purely because of the solid defense positions deployed in advance. The problem is, even relying on the solid defense positions, his troops are extremely passive when facing the offensive of the Tang Army, unable to resist.
The crux of the issue is, even though the Tang Army has only been attacking for five days, Felix's carefully prepared defense line is almost completely lost: in the deepest areas, the Tang Army has pushed forward several kilometers, nearly reaching the third line of defense.
If the third line of defense is breached, the subsequent battles will have to be fought in the open field against the Tang Army. This is not what Felix wants to see, because he has no confidence in stopping the Tang Army in a field battle.
