8" drop should be fine.
Try filling the water tank and measure again, just to see if adding 600 - 800 pounds of water makes the rear of the RV sink about 2" more.
You would not want the 10" drop anyway, because it will scrape on any driveway when you go into them or out of a gas station.
Also try measuring the hitch, when it is basically level, say propped up on a box or something while attached to the Honda. See how high the ball mount would be while level.
A uphill tilt to the hitch is OK, because in a panic stop, the front of the car will try to push up on the hitch a little bit. But 10" of tilt, and it can go under the RV. So keeping it level is safer. With the car higher than the hitch ball, a panic stop can cause the car to ride up over the hitch, a very interesting situation.
Fred.
