I'd call that a mistake, but what ever floats your boat.
Honestly, I only see 2 choices here and that would be a RPM or a M-1 single.
Other dual plane may apply, but it is the same idea as a RPM and which one squeeks out 5 hp can scream winner. (LOL 5 HP, big whooop! But everybody makes a big deal about the most minor things.)
