Having towed trailers for the last 35 years, the height of the top of the ball really depends upon what is required to make the trailer sit level. On most full sized trailers the height of mine is between 18 and 20 inches, but my little 4x8 footer is only 15 inches. For my big Dodge Diesel 4x4 I have a B&W adjustible hitch that allows me to set the best height, and my Reese w/weight bars also allows me to adjust the hitch head height. With the Forester since you will not being pulling a tongue heavy trailer (I hope) measure the trailer's needs and purchase according. By the way, the hitch on mine is to have something to tie the kayak to.