I replied to a post yesterday that I was having the same issue as the person who opened the topic.
The screws holding the mounting brace were causing the mounting plate from sitting flush with the junction box. I took everything apart and apparently I was having a brain fart. When I attached the brace tot he recessed set of screw holds everything fit. Even though the plastic mounting plate does not fit as snug as I would like. It bends easily. I don’t think any rain will get in. I have only been doing electric for 40 years, What a bonehead move. Sorry for the bashing, but I still think the mounting system could be much better.