Well, here's the thing - by thinking about 'direct[ing] the army in battle', you're imposing a later conception of the king or general's role in leading the army. In that period, a king or general is not just expected to lead from the front; doing exactly that is how he motivates his men.

u/Iphikrates of course has posts covering this: on Greek generalship and the relevant mechanics of battle, and on how Alexander led his men.