Any scenario with randomly variable reinforcements will always be impossible to balance. High replayability, but low consistency of results. The Sassanids (nor the Byzantines) will never be sure what reinforcements if any are arriving.
Thematically, the Byzantines were breaking out of a strategic encirclement, and the Sassanid generals were very concerned about the Byzantine army heading deeper into Persia. Shahraplakan had to race his army through mountainous terrain to intercept Heraclious, with forces strung out on the march. When he did intercept, he had to accept battle on ground of the Byzantine choosing. This was exacerbated by Byzantine false flag deserts spreading news that a 3rd general, Shahin, was coming with a 3rd army, which heightened the competitive urges of the Sassanid generals to claim sole victory and not share the glory. Shahraplakan gambled here and lost.
wise and full of devices
