What i noticed in an earlier version pre 1.82....
I was at war with the Korath and they were sending powerful fleets against me.
I was able to deal with them ok, but when my fleets started getting noticeably more powerful, that is when i noticed a change in their behavior.
They started 'sneaking' fleets through wherever i did not have sensors, and sometimes manage to destroy one or two starbases before being intercepted.
Somehow the AI knows exactly where i do not have sensor coverage - that is a fact!, then as soon as i put a sensor boat there, they immediately stop trying to sneak through that area - how do they know i put a sensor boat there when they have no fleets in the area at that time?
Further.... once i have full sensor coverage along the boarder, they stop sending fleets altogether, they don't even take a peek, my sensor boats are not activated from sentry mode.
Just out of curiosity i take away one of my sensor boats and leave a 'sneak' path to my starbases.... and sure enough they come that way, its amazing!!!!