I agree on the result, but I believe it should
not be the task of the player to show such a behaviour by his nature, but it's the task if the game (mod) to enforce such behaviour on the player. He should simply be better off leaving those units behind, not skeleton garrisons - for many reasons, be it defence from the AI incursions, potential rebell attacks, or keeping the order in the settlements. For instance, the high unrest levels may do the trick - I'm forced to have many troops in the settlements in the SSHIP game (you
may see it in this table: number of units and troops, and also the garrison costs). The free upkeep is also beneficial providing the player with positive incentive to keep the units at home.