Just having reread all of this I realized that there is an uncanny parallel between this new contra piston design and tapered cup expansion plugs or "Welch Plugs" that are used in full sized engines.

Couple that with the twice mentioned top of the cylinder "the contra piston end will just enter the top of the cylinder bore" and "and pressed into the cylinder top" and its not hard to believe that the contra was 'meant' to be installed that way.