18 yards does seem close for a point-on distance.
Do you need to be shooting 31" arrows? You didn't mention your draw length.
Do you move your head around when you aim? I wonder if you're doing something to move your eye down closer to the arrow. I was taught to keep my head still and upright and bring the arrow to it, but I know some people tilt their heads when they shoot to get their dominant eye over the arrow, and they seem to do fine too.
My primary anchor used to be the back of the cock feather against my nose, and my point-on was just under 40 yards. I changed about a year ago, and now draw the feather under my nose so it anchors when it touches my moustache. That increased my draw length about 1/2" and also increased my point-on to just over 40 yards, since my anchor point is a little lower. I shoot 29" arrows with a 28" draw length.
Basically, your point-on is a function of how far the arrow is below your eye, and the trajectory of your arrow. But, as you said, your arrow doesn't drop that much in 18 yards, so the only variable is really the distance between your arrow and your eye when you aim, for a given bow and arrow. So if you want to increase your point-on, you'll have to do something to increase that distance. Of course, as you get it out to 40 yards or so, the arrow trajectory will come into play, so you'll increase your point-on even further by shooting an arrow with flatter trajectory.