The RPAU does not come with a ceiling plate. Once you add in all the hardware (especially in the universal version), the RPAU isn't very flush against the ceiling. However, that is a good thing! Mounting too close to the ceiling puts the projector in a pocket of hot air and really kills the cooling, especially if there are other obstacles (bulkheads, shelves, lights) around it to trap the hot air. Also, the more flush you make it, the more vertical lens shift you need to use to get the image in the right place.
The RPAU is built like a tank, it's sort of over-engineered to the point of hilarity. I fully recommend it, and even adding a 3" NPT pipe to drop the projector even lower if it's cosmetically feasible.
I had a very flush mount for my 8350 (Omnimount), and I'm pretty sure that's what cooked my polarizers after only 830 hours. It ran incredibly hot, I thought, but I didn't know better. I changed things up for my next projector.