Make it a setup option when you start the game. No reason not to be able to choose at game launch right?
Yes, there are lots of reasons not every minuscule feature should be a setup option in the start of the game. The primary 3 reasons if you ask me are:
1.) It makes it even harder for new players to get into the game and setup their first game without spending 10 hours trying to understand what the setup options means.
2.) There is limited space both on the start new game option panel, and on the mouseover tooltip that is supposed to explain what the setting do.
3.) Not every minor detail needs to be controlled here IMO, and adding it would be a waste of development time better spent on other things.
Don't get me wrong, I do love setup options. But I can think of dozens of other options I'd much rather have instead that actually impacts and influences how the game will play to a large degree.