We made a "Photoshop" analysis and the magnetic part has a radius of roughly 13mm (0.5118 inch)
Apple customer service told us to write to the mFi support team and this is what they replied to our mail:
"At this time, development of hardware intended to be compatible with Apple Watch is beyond the scope of the MFi Program.
For app developers, an all-new platform, WatchKit, has launched: https://developer.apple.com/watchkit/."
Kind of a bad answer.... Watch Kit is definitely not for hardware/case/stand developers.
Does anybody have better connections to the Apple hardware department/service?