Aubrey passed on this gyazo in a different thread. Thank you Aubrey!
I think this does show that Magic Reef is recessive to Dreamy Mirage.
First you need to look at the pedigree above and realize that Gavan is a Proven Magic Reef hider.
In this pedigree you can see that Gavan has been mated with Snowflake - Showing the Dreamy Mirage which is recessive to Gavan's shown Exotic Journey. The kitten shows the Dreamy Mirage. Gavan could not have thrown Exotic Journey or we would have seen it on the kitten. Therefore Gavan must have thrown his hidden Magic Reef, which hides underneath the Dreamy Mirage.
Therefore, Magic Reef is recessive to Dreamy Mirage.