Daas,
As per Tanya, I think he explains that there are two terms of Tzadik one is in terms of Madrega/level and one is on acts i.e. as he explains:
??? ??????? ????? ????? ?? ???? ???? ?????? ???? ?????? ???? ????, ??? ?? ?????? ????? ??? ?????, ??? ????? ??? ????, ????? ???? ????? ???? ????? ????. ??? ????? ????? ?? ????? ?????? ?? ???? ??????? ?????? ?????? ????????, ???? ??”?: ?????? ??? ??? ?????, ?????: “???? ??? ?????”, ???? ?? ??? ??? ?? ???? ??????.
Perhaps that is how he will explain the above.. or its all relatively speaking. How would you explain David HaMelach “sinning” as per Tanya?