Interesting. As I'm sure we all can attest to, there are certainly times where ice defines a late game naval strategy (should one be necessary) so I'm glad I learned this! While it most likely won't be relevant in my current game, I'm (finally) doing quite well on monarch and it's a great feeling. The current head-scratcher is timing expansion, as I've gone quite wide and am dominating on land, though my tech is lagging pretty seriously at this point. It's late medieval so I'm awaiting to see how impactful entering the renaissance and getting the finance techs and infrastructure will be.
But anyway... back to the point: Snowgerry, how about a WB scenario? I can set up a duel archipelago map, give the other civ destroyers and their upgrades, and myself age of sail ships which are bound to lose, and cleave the "prime meridian" with a solid line of ice, enter the game and then DoW the civ to see if they know how to move through it. If no one else would like to try this I'd be happy to this weekend. I know nothing of the inner workings of the AI or about its programming, but it seems to me that this is a pretty surefire way to test it.