The Tang Empire, although not directly engaged in combat, did indeed provide a great deal of assistance to the Fengjiang defense troops. For example, the Tang Empire's individual soldier communication system played a significant role in this battle.
The Tang Empire's frontline observation posts carried communication equipment and professionally reported the exact locations of the Dahua Empire's attacking troops.
Thereafter, Fengjiang's artillery needed only to take charge of firing. Their shells would blanket the enemy, instantly inflicting heavy casualties.
The Dahua Empire's artillery also tried to suppress the Fengjiang defenders' guns, but due to accuracy issues, the effectiveness of this suppression was actually very limited.
The frontline battle was still fiercely ongoing; the Dahua Empire's troops could not possibly crumble and give up this attack opportunity just because of a round of precise artillery fire.