What is the average position for tb2l teams promoted champion?
CREATE TABLE "season_by_season" (
  "season" text,
  "tier" real,
  "league" text,
  "pos" real,
  "postseason" text,
  "turkish_cup" text
);
SELECT AVG("pos") FROM "season_by_season" WHERE "league"='tb2l' AND "postseason"='promoted champion';