-1
I don't think it makes sense for an army to require extra provisions, because every party in the army already has their own provisions. It's not like they'll suddenly need more provisions just because they're marching together. I think the best way to create a new money sink is to greatly increase the cost of troops advancing to the next tier. Think about it - when a troop advances, they may go from leather armor to plate mail in an instant. From where did the armor come from? Their wages surely didn't cover it -- you had to buy it for them. That kind of money sink is renewable as you'll always need new troops to replace dead ones.
I don't think it makes sense for an army to require extra provisions, because every party in the army already has their own provisions. It's not like they'll suddenly need more provisions just because they're marching together. I think the best way to create a new money sink is to greatly increase the cost of troops advancing to the next tier. Think about it - when a troop advances, they may go from leather armor to plate mail in an instant. From where did the armor come from? Their wages surely didn't cover it -- you had to buy it for them. That kind of money sink is renewable as you'll always need new troops to replace dead ones.