Your ct200h is pretty much identical to my corolla. I have the prius drive train too. The biggest difference is that I like mine, lol.
If I let it run the hybrid system automatically, yes, 30 mph is about right for battery kick out, but if you turn the cruise off, you can force engine shutoff by quickly pulling your foot off the gas pedal to shut the engine off, and ease back into the throttle just until the engine starts again.
Climb a hill with the engine and you can coast for quite a long time on battery if you're careful.