Flakbait, I think your looking at this the wrong way.
Field ownership (to a particular country) is assinged in the arena setup. Its not something you do when constructing a terrain.
What I mean is, say you want to add the default small airfield to your terrain.
1.) Go to Edit Object Mode.
2.) Select the point where you wish to place the airfield within the terrain. Make sure its the center of a grid square.
3.)Select the small default field in the object group field, and then add it to the terrain.
4.) Then like I said before, it will ask you which field you wish to assign ownerships (note: assign ownership to a field, if you select country, whatever you placed will not be capturable).
5.) Field ownership field will look like this:
F1
F2(new)
This will be a new field so you select F2. Now that means that everything you just placed is assigned to field 2 ownership.
6.) Now say Field 2 is currently Bishop and you want it to be Knight. You go into setup, and choose field assignments. And change the field ownership to country Knight just like you do in a H2H game.
Its especially important to note that the only objects you wish to assign ownership to a country is the City, HQ, Factories, and other Strat objects. All airfields and vehicle fields, should be assinged within "Field" ownership, so that they can be dynamically set in the arena setup (when its actually used in a game arena) and can be capturable (change country ownership).
Does that help any?
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Vermillion
**MOL**, Men of Leisure
"Real Men fly Radials, Nancy Boys fly Spitfires"