So you’ve got three different magnetic tail caps, right? The first one is green (wrong dimension), the second one is green (very wrong, it’s for SC31 Pro), and the last one is black.
The black one is the correct size, right? Does it have the same type of construction of magnet and spring as the first (the wrong) one?
I’ll be very grateful if you could upload pictures of the original (non magnetic) tail cap and the black magnetic tail cap. Specifically the inside of them, showing/comparing their springs etc 
I’m still considering the possibility to install a magnet inside the regular (non magnetic) tail cap.
Although, for practicality and usefulness, I think magnet outside the tail cap is actually better (larger diameter, completely flat tail, improves tail standing).