I have a 9 1/2 Host. I estimated the length when I originally bought mine. That was ok, but it extended past my bumper which was a bit of a pain to leave on since it impacts walking down the steps. The fix is to cut it off which is also something else to do!
If I was you, I'd install the hitch and measure after it is in place to determine where you want the end of the hitch to be when the ball mount is off.