As Pete describes, the counter is quite conservative. The amount an image can be compressed depends quite a bit on the image. An image with a lot of detail and a lot of different colors results in a large file even after compression. Since the camera does not know what you are going to photograph, it takes the conservative approach. In practice, 14 bit compressed files range from around 20 MB to 30 MB, so your experience is in the normal range.
If you want a smaller file, 12 bit does work. It's a good bit less forgiving of heavy cropping or recovery of shadows, so is more like a JPEG with a little greater ability for post processing.