Almost 4 and still having (poop) troubles

fiasco

My son will be 4 in November.  Been in underwear for a year.  Can't remember the last pee pee accident.  Probably like 6 months ago?  But he isn't ready to night train yet and still naps, so he wears a pull up to nap.  He poops in his pull up at nap time about 80 % of the time.  He gets a sticker any time he poops on the potty instead and then chooses a new toy when the chart is full.  He poops whether he actually sleeps or just quietly plays in his room.  Whether I leave him in undies or put a pull up on.  It makes no difference.  What am I doing wrong?