Auxillary Engine 9.9

I am in the process of installing a 9.9 and have a question of where to the mount the bracket in relation to the prop/caviation plate depth. I can't mount the bracket where when it is adjusted down the prop and cavitation plate will be fully submerged in the flow of water running from under the hull. Given that it is a small auxillary engine does it matter much if the caviation plate and prop are in the water at the right depth but the bottom of the transom but not in the flow of water?

Thanks