Yeah, like I said, it doesnt work that way on this map you have to go center out, because the core can spread it wherever it wants on the map.
Again, when you are solo the spread is suppressed, so while it can happen it doesnt happen often. This is why you didnt notice when you were alone but did notice when Imaginary joined as it happens more frequently.
Make a ring with the broken Anchors and fill in the inside is the best move you can make on this map if you cant take out the Core.