that might be something that is tied into the core game files so a mod wouldn't over-ride. i know tweaking amount of villages in a starter zone was only changed when i went into the game core files.
also focus more on dust then, or exploring ruins and get that xp. if your army isn't fighting your paying the upkeep for almost no reason.

Yes I also realized that, thank you for your comment with nice suggestions. In late game, getting huge amounts of Dust is possible and army's upkeep can be neglected easily.

However, in early game army upkeep has big impact on economy, also I would like to have more battles too, which player and AI can spam more soldiers to the field without ridiculous upkeep increment. We can consider the increase of upkeep as larger salary to soldiers for their higher experience. However, at current levels, these are big salary increases, also when we include ridiculous salary of Hero as he/she levels up, the impact is doubled.