Sea zones don’t belong to anyone, so convoys don’t belong to anyone. If you have a ship in a sea zone with a convoy marker that’s adjacent to an enemy’s territory during his/her collect income phase, you reduce his/her income. It’s as simple as that.
I love this new rule, Kev. Was it Mons that come up with the idea ? Anyway, lets take an example:
UK controll Kwangtung (3IPC) and Japan controll Formosa (1 IPC)
UK has a sub in seazone 20 and Japan has a sub in seazone 20. This is legal according to the rules.
The Japanese sub deny UK 2 IPC income, and in next turn, if still alive, the UK sub deny Japan its 1 IPC income. This happens because convoys belong to everybody that control any adjacent territory, right ?