Nowhere in my settings do I see an option to control container size. Regardless though, when I choose to fit to container at least on my laptop's limited screen it makes it too small.
What I've ended up doing is setting it to fit width and then changing the window size itself so that it automatically makes the "width" it's trying to fit smaller, and thus sizes down the image a bit. It's mildly annoying since I'm used to keeping windows I use on full screen, but it's not the end of the world.