If you're iPad is wifi only, then it does not actually contain a GPS chip. This places some pretty big limitations on location detection, though the iPad will still use its knowledge of wifi access points to try. So this may be what you're seeing. Also, GPS quality can depend greatly on local conditions and the weather.
What I've always done is to workaround this in my design with an understanding that location detection will not be perfect. For instance, in Mentira, where we were using iPod touches, there would be an initial plaque with a large radius, maybe 50m. This would provide players with instructions to go find a particular thing in the environment and use this information in the scanner or decoder, usually something like a address on a mailbox, for the "real" game object's trigger.