How can I increase the size of my game window in cinematic mode?

My game code automatically handles adjusting to the current window size. But when my game is running on kongregate.com, the game window doesn't increase in size when I press the Cinematic Mode button. Is there a way I can specify the width and height to use for Cinematic Mode or something else I need to do to get this to work?

Note that my auto-resizing code does work when I run my game in a browser outside of Kongregate and when I run it on Facebook as a canvas app.