I have had this discussion with Patrick before.:)
8.22 In order to interdict, a player must have at least one Fleet Point in
the Sea-zone for every two Fleet Points the enemy has in that same
Presently, the software lets you interdict if you have one fleet no matter what your opponent has. Example, 1 German in the Atlantic interdicts against 4 Wallies.
I also contacted Rick Young on this, he agrees that it is a ratio thing even though the rule does not specifically say ratio. So, 1 to 4 cannot interdict. 2 to 4 can interdict. 2 to 3 can interdict. etc.
There should be an option in the Settings(on the top menu bar) to opt for either of these interpretations. This way we keep everybody happy.