Weight centered over the axles will add 0% to the hitch weight.
Weight added directly over the ball will add 100%.
Between that it's basically a percentage of the distance between...so 50% of the distance between the ball and center of axles will add 50% to the hitch weight.
Now if you can move weight from the back end to the front end, that can actually result in greater than 100% as weight behind the axles actually reduces hitch weight. So if you have a generator on the rear bumper and can move it to a rack above the tongue, that can have a bigger impact.
If it's towing well, I wouldn't put a lot of effort into it but do keep an eye on it...especially if you have a trip where you will be carrying fresh water. It might not take much to push from towing well to being a problem.