Apart from the probable lack of Housing and Amenities (the latter if you don't build the Colosseum) early on, you can surely go wide and tall. However, there's also no super-advantage doing that either, because districts take quite some time to be completed, and you don't have many tiles to work if you want to pack cities together to use the Factory bonus.
The radius itself hasn't changed. What changed is that only the highest-yield Factory bonus will count for a city, even if that city also has a Factory. That means that you seek now minimum overlap instead of maximum overlap.
I've never seen it up to Emperor, and I doubt it does it on Immortal and Deity given the amount of work needed (and lack of hurry) to get the Great Scientists for a Science Victory.