Leave them size 6, but if on a river then they can be bigger, (almost*) never build hospitals in corrupt zones, it's a waste. Make everyone that is not making just enough food to keep the place fed a sci/tax and don't build anything there except maybe a market in your bigger than 6 towns.
Don't forget the entertainment slider is subject to corruption, as MAS said, but luxuries are not subject to corruption, so a lux conected to all cities will count equally in all cities, which is why the entertainment slider is a necessary but temporary solution to serious happiness problems. You're at war, capture some luxuries for the people back home.
And, anytime you use automation of any kind, it is wasteful.
Here is a shot of a modern science farm, on a river with all the luxuries, no improvements are necessary and you won't need to check ever again unless you want to. With less luxuries a market might be necessary, but that's it.
The five people make all the food needed, the other seven generate science.
* you only build hospitals in corrupt towns when you are trying to "milk" the score for the highest possible score, please refer to
Maximizing your score by SirPleb