Zone of Control in past civ games was simply a means of restricting movement. You can't just waltz on past the fort, ecspecially if there are other units near by.
If you took the other unit off my diagram, the 'A', then the enemy unit could move south east making the zone of control less useful. It makes forts really nice when they are used together. A fort every 3 or 4 spaces with a few other defenders back a bit to impede movement further can make it very hard for an invading force to enter your territory without addressing at least one of the forts.
They did work this way in one of the past civ games, and I really liked the way they worked.
I don't like the idea of giving them a maitance cost so you can build them on improvements. I think that would actually make them worse. I think I'd prefer an additional unit over a fort for that maintainence cost.
If you took the other unit off my diagram, the 'A', then the enemy unit could move south east making the zone of control less useful. It makes forts really nice when they are used together. A fort every 3 or 4 spaces with a few other defenders back a bit to impede movement further can make it very hard for an invading force to enter your territory without addressing at least one of the forts.
They did work this way in one of the past civ games, and I really liked the way they worked.
I don't like the idea of giving them a maitance cost so you can build them on improvements. I think that would actually make them worse. I think I'd prefer an additional unit over a fort for that maintainence cost.