Hardwired Kit for Spotlight Cam help (UK)

This is my first experience with Ring products. I have bought a Spotlight Cam and the Hardwired Kit. I have tried to understand how to install this using the online guides. However, I am not sure why the ‘round junction box’ and ‘round box cover’ are built as they are . I also have a slightly oversized black gasket in the kit.
The reason I am writing is that the four fixings on the junction box, for the cover, are not all made the same: two are flush with the top edge of the junction box, two are recessed. The end result is that the cover does not fit flush to the junction box. Is this designed like this (if so why) or, do I have a faulty junction box? Also why is the gasket oversized?