who told you you can't do that? There may have been a coincidence that someone tried it out with a new engine made for the USA market. These have a lower compression ratio, and need nitro. He may have obtained low reading because of not using any, not because of the rear exhaust configuration. Of course you need to know how to tune an engine with prop, nitro content and exhaust system.
Go ahead and do your thing.

edit:
quickies first had black heads, then gold, now blue.