I have talked to a few people about that same thing including Champion and RJC.
Champion's response was in the neighborhood of is could work but not sure.
RJC's response was, it was designed to be used with OUT a spacer we can't test all the different size spacers out there.
some guys say get rid of the PP.
Others say keep it.
I am going to keep the PP with my spacer just not sure of above or below the spacer.
From what i understand the PP is designed to change the plenums characteristics-- So i might go Plenum, PP, spacer, intake manifold.