The reward for battle is influenced by the class of the selected unit.
The light unit class is the cheapest to maintain and the best to earn game currency, but the use of such equipment brings little battle experience.
Medium units are more expensive to maintain, so they are less effective at earning game currency, but bring more experience.
Heavy units are very expensive to maintain, but gain the most battle experience.
It turns out that in order to earn game currency it is better to use light units, and then go into battle with medium and heavy ones to gain experience and tournament points.