I feel that the very small bore needs as much mechanical leverage as possible, as early in the power stroke as possible. The shorter the rod ratio, the more angularity is achieved in the stroke.
Think of it this way. If you were to try to rotate the crank by hand, by pushing straight down on it from a journal placed at TDC, it would never budge. If you kept your hand in the same place, but tilted your arm, the crank would spin. The more angle to your arm, the less effort it would take to move the crank.