I am not sure about P5 since I haven't purchased it yet, but I have had the same problem in P4. I find the obj files that have large flat planes or nice square edges always ballooned (additional smoothing) on import. But, I have learned that 3ds files always come in nice and clean with no or minimal ballooning. Perhaps you can take your model and convert it to 3ds and re-import it, then resave your prop to the library or to an obj file.