Why does shortening my prop shaft lift boat?

As title suggests, just would like to know why when I chop down the prop shaft In my midmount speed boat, and move the propellor further under the boat, does it lift the boat higher in the water?

 

OK here is a wild guess. Our power boat guys can explain with more authority.

I presume that the speedboat has a prop shaft that is aiming slightly downward at some predetermined angle. There will be a lift factor at or near the prop location. Generally the prop action tends to impart some lift to the aft end of the boat. Move the prop forward and the lift center is moved forward such that the boat tends to rise or at least to create that impression. A vector diagam would imply that this is the case.

Moving the prop forward has some other implications that may or may not be desirable.