I never thought of it this way. I'm American and I can understand fluent English speaking Europeans way better than I can understand British, unless that British person is from London. 70%? That's optimistic. I don't even think I am understanding words, only the most likely context in the flow of a conversation and the most likely way to react.

Fluent Northern European English (Belgium, Netherlands, Scandinavia, North Germany) almost blends into "normal" English to me. It is kind of shocking.