After some research and looking into the specifics of the circle of protection a bit, it seems like the reflection isn't actually luck based. According to the [Circle of Protection entry][1] in the BOIR Wiki, the item:

 > Surrounds Isaac with a large white halo around him that pulsates.
 >
> - With each pulse, the halo deals contact damage to enemies equal to Isaac's damage.
>
> - **Each pulse converts any enemy shots touching the ring into friendly purple homing tears that have Isaac's damage and no other tear modifiers.**

This can be seen if you check out the [video of the item in use][2] on the wiki page. When an enemy tear enters the ring just as it is getting brighter it gets reflected, otherwise it passes through as normal.


  [1]: https://bindingofisaacrebirth.gamepedia.com/Circle_of_Protection
  [2]: https://www.youtube.com/watch?v=iTAksu-4MTM