Hitch Height vs. Ball Height
You may find that the weight of the trailer on the ball will bring it basically level... As Robert pointed out, your goal is to achieve a level tow vehicle and a level trailer. Hitch it up and take some measurements. Assuming your ball height is 19" and your coupler is 18" as measured from the ground to the top of the socket, you're in the ball park. Depending on your tongue weight, truck spring rates and a weight distributing hitch if used, will all determine how level everything sits. From there you can decided if you need to get a mount that raises or lowers the ball.