being it shot fine at 20yds,its YOU.maybe
you have to squeeze and watch arrow hit target at 30/40.

dial a range can work but you must check it all time,rope cocker moves dial when you are cocking.

i assume you used the no.3 setting on the dial a range at 30 yds.
try shooting at target at 20 yds and use the no.3 setting.

this should tell you if something is wrong with no.3 setting.

if all arrows GROUP great at 20,ITS YOUUUUUUUUUUUUUUU.