Having experience doing this I would say I probably wouldn't do Montis on the back as it makes it hard to work on the tank and you are always worried about knocking it off. Anything that encrusts should work over time. I've seen xenia on the back before and GSP. I've also has an encrusting gorgonian on the back wall which is similar to the psp.
I had a rock with some gsp on it I had forgot about, it was in my smaller tank near the back. LOL.
I cut some off and glued it to the back glass. Also glued large pieces of cap to the two corner over flows.
Thanks guys.