I believe it checks for mobile human strength as many as 3 hops away. Previously they didn't check nearby strength at all, and it was very, very easy to bait waiting threat and kill it at leisure. It's still possible to bait them, but it's not trivial.
Anyway, if you wanted to test it, you could try scrapping your fleet. Presumably they'd attack then, if there was something worth attacking on a planet with little/no turrets. Bear in mind they're scared stiff of Fortress units.