if the groups are good and to the right at all distances, and things seem to be in order except the sight won't adjust far enough...a right handed shooter can move the sight to the right by putting a spacer between the sight and the riser. mind you, this is probably cheating as the bow should get a proper rest and total tuning. but it also might work, so wth?
if the bow is shooting straight at 20 but goes right at farther distances, get a plumb line and check the sight for level, which is sorta what Old Dog beat me to saying.