From what I recently read on the web, distance is present in EXIF data when the used lens has distance reporting capabilities. A list of those lenses has been published by Chuck Westfall back when ETTL-2 was announced. However, a dissection of decoder rings (
here) seems to indicate that a range of distances is reported rahter than a exact value. This might explain why you find you distances somewhat weird.
Please, note that I'm not a specialist in decoder rings