Some motors actually run better with the smaller hub size. My dad's Ranger 519 with 225 Mercury was propped by a guy who used to race boats before we bought it. The best prop he found for the setup was a Trophy Plus for a 150 gearcase. This might be an application that it doesn't work well with, but there are some that it helps to do that with. 

my mistake.  I just looked at the prop on my Optimax, and it looks like yours in the photo.  The prop hub has a sleeve which fits into the lower unit housing, preventing excess exhaust from escaping.