I suspect that the smaller key grip and the smaller remote both correspond to different technology in the car. My thinking:
My 1992 Civic key looks just like my Insight key, except that the Insight key grip is about twice as thick. That's because of the security device in the grip of the Insight key that won't allow a mechanical copy of the key start the car.
As for the remote control key fob, note that one button that locks or unlocks the car means one frequency or code pattern to trigger the toggling locks. The American Insight has two button (two frequencies or code patterns) -- one to lock the car and the other to unlock it. It also has a third frequency or code pattern to set off the "panic button" flashing lights and horn.
You might like the smaller key fob, but likely it would either lock OR unlock your car, but not both, and you'd lose the panic button option. I think the key matches the car. I doubt you could just replace the key without doing an electronic modification to the car's security system.