It depends on the game, and its settings. If you've got a map that takes up full screen, or the majority of the screen then it would probably be better to use larger more detailed icons.

If the map is smaller, the icons should be smaller. If it's a retro game, it's better to go small either way, and just stretch the icons, or make them seem like they have the stretched vibe.

It really just depends on the game, but there's also a matter of the artist. A big base might suck compared to a small base, if your pixel artist only knows how to draw and animate a small base properly. After all, a big base means more detail, which means errors are noticed easier.

You're welcome. Good luck with anything you may be designing.