Is the agent-placing requirement actually spelled out anywhere, or is this something people have figured out through experience?
The lack of a sturdy in-game help/manual system is probably my single greatest gripe about GC2. Your basic question about espionage was all over the forums around the time DA was released, but if I'd been depending on the PDF and the game UI, I'd have been left with too many questions for too long.
One of the most radical sets of changes from DL to DA was espionage functionality. The devs replaced the budget-centered view with a unit-centered view. For many of us, this introduced a major frustration: in DA, you can't gather intel without directly harming the target. On the other hand, before DA, you couldn't do a thing with your intel spending but read reports.
I hated the change at first, but now I want both options. Also, I could *almost* swear I read some TA rumours that the expansion would restore budget-based, non-aggressive intelligence gathering along side the sabotage agent system. But maybe I'm confusing my own past pleas for change with casual chit-chat about dev plans.