I have long thought there should be one general spy DR and one op-specific DR so that it becomes very difficult to do extreme amounts of one op but that you can do a couple of several ops with less pain than today.
10k acres with 200k spies fail most ops today against 100k acres 1000k spies. That wouldn't change at all with the proposal.
You can't go so low as 10 acres or 100 acres because there can be limiting constants just like on the tech formula etc. We would delve into a discussion that has nothing to do with most real countries in the game.