Like the company rep said, 20 yds is probably too close for practical use with a scope on your gun, especially if there's over an inch or so between the height of the scope and the center of the barrel. You may have noticed that most scopes designed for a .22 sit very low on the receiver/barrel. However, the height of an optic on a 15-22 is usually a good bit more due to it's AR style design. If you think you really need a scope assist at that distance, I have no good reply for you. Instead, I'd recommend using the iron factory sight for close (less than 100 feet or so) shots and optics for longer ranges. I have the red dot and a laser on my 15-22 set so I see the iron sight through the red dot and they all zero/converge at about 30 yards. A friend has a similar setup to mine on his gun but has the laser set to zero in at 75 yards.
"... Americans... we want a safe home, to keep the money we make and shoot bad guys." -- Denny Crane