Holes 1 inch apart is telling you that you're okay within a half inch or so.
First thing to do is to measure (while on level ground) from ground up inside the coupler to where the top of the ball would rest when hitched up.
Second thing to do is to figure how much your tow vehicle will settle when the hitch weight is added to it. Measure fore and aft reference points (license plate bolt or something to ground) then have a few friends get in. See how much the reference points have settled.
Then adjust the ball mount so the ball is at the needed height for the coupler plus however much the rig will settle under load.
for some ideas and links. Keep in mind Dallas's guidelines
"Adjust the hitch ball height to 'level' the trailer
Adjust the weight distributing bars to 'level' the tow vehicle
Adjust the hitch head angle to 'level' the bars."