You can set it up in the DW in order to have the clearance to clear your sloped apron but i would set it up correctly in the street or a level lot.
It can take awhile to set it correctly because you need to load the truck up for a trip for proper ball height and make multiple adjustments that may take an hour or two.
You need to set up the hitch on level ground so you measure the bottom of the frame to the ground, front and rear. Do not use a level, take measurements.
Then you should drive it to test it . Sometimes you need to change the ball to a long or short shaft to gain or lose an inch of height.
Do it right , you won't know its back there.
http://davidsrvtips.blogspot.com/2009/02/hitch-setup_2781.html